Rave's Passat 1.9TDI - 3/2/20 More alternator bodgery

[Dave_Q]

Oil in the inlet is normal, they deliberately vent any crank fumes into the inlet because of emissions.

 

It is the intercooler that's behind the light there. 

 

Hopefully the hose will fix it, black smoke is typical with a boost leak as the ECU is still sensing the airflow into the turbo, but it doesn't make it to the engine, making it v.rich.

[Rave]

Fingers crossed. It would explain the crap economy on the last trip as well if 15% of the fuel was coming out of the exhaust unburnt.

[Rave]

Had a bit more of a fiddle with this today. First I wanged a bit of teflon tape under the seals in the post-intercooler inlet hose. Felt pretty tight when I reinstalled it. Took it for a test drive, and still plenty of smoke on boost. If anything though it seems to let out a big puff of smoke when you release the throttle, although that could be just a coincidence due to how the air gets sucked round the back of an estate (they apparently have a sort of Kamm tail effect), I was only accelerating between speed bumps in the 20 zone roads round my house.

 

So then I decided to take the inlet hose off the turbo, which resulted in a lot of swearing, especially when I dropped my 1/8" wrench down onto the undertray. I think I'll be able to fish it out with my magnetic tool, although TBH I should probably get the car up on ramps and remove the undertray anyway. I can't see into the turbo without a mirror, but there was a bit of oil in the inlet- is that normal? There's a pipe that comes out of the head and down to the inlet hose just before the turbo, which I guess might be the crankcase breather, I suppose it makes sense to vent to the low pressure side of the intake rather than the boost side.

 

I made sure my fingers were clean and reached in; there's no end-to-end play and side to side play seems not unreasonable for a plain bearing turbo- I'm typing this after coming in to google it, as for some reason I had thought that end to end was OK but side to side was bad- I don't think mine is unduly worn, you can certainly feel some wobble but not much more than a millimetre I'd say. The turbine feels a bit lumpy when you spin it, mind.

 

I guess the next step will be to clean all the shite off the turbo outlet hose and see if there are any obvious splits in it, and if not get under the car and remove it for a closer look, that seems pretty easy from a youtube vid I saw. Not sure what I'll do if I can't find a boost leak anywhere, give up and take it to a diesel specialist I guess.

[dieselassist]

...I fitted an 'new' (to the car) tank lift pump, to my 04 audi a4 avant PD 115bhp during the week, in the hope that its help its cold starting efforts; basically it didn't like a start where it was parked on the flat, overnight or whatever, n wouldn't start when it was parked like that; the old lift pump was black with an oily residue n I drained/siphoned the tank as I let it go low before fitting the new lift pump .....anyways its seems 9% keener to start with the 'new' (secondhand bought for €15 off a polish lad who was breaking one)... but theres still a few seconds of 'chugga#chugga' before it catches... 

 

...I still leave it parked on a slope which ensures it starts; cars this era here are pretty much worthless so not worth getting a diesel specialist involved in my case; @ €80 just to book the car in to them; its taxed so i'll get the winter out of it...

[Rave]

Bit of an update. On Monday I stuck the Passat up on my ramps and pulled the undertray off. If then started raining and continued all yesterday, so it wasn't until today that I went under for another look. It's all absolutely covered in oily shite under there, so working underneath it was jolly unpleasant as I kept dislodging great gobs of it into my face. However I removed the turbo outlet hose which goes to the metal pipe that runs across the bottom of the car, and the short connector hose that goes from the other side of it to the intercooler, and found that both were in good nick despite looking like they'd not been removed for years, or probably ever. While I had the turbo hose off I used an All Purpose Poking Tool to push up on the VNT actuator arm from underneath, and found that while it takes quite a lot of force to move it (I'd estimate around 10kg) it does seem to move freely and return under the spring pressure with no stiction. The intercooler area was particularly covered in loads of wet looking oil though, so I do wonder if there is a leak somewhere round there.

 

 

With the hoses reinstalled I decide to take it for another test run just in case my prodding and poking had fixed whatever the problem is/was. I didn't bother starting the engine to roll it off the ramps as my driveway is slightly sloped. With it halfway across the pavement and the road I then tried to start it to park it parallel, and the battery died after about 15 revolutions. Of course at that very moment a local authority school bus pulled up, so I bruised my shoulder trying to push a 1.6 tonne car far enough out of the way that it could get past. A heated search of the house failed to turn up my jump leads, so it needed the combined efforts of my wife, father in law and I to get the bastard back on the drive. I then went to remove the battery to give it a quick blast with my old dumb charger, but it turns out that that requires removing the wipers and the windscreen valance, so in the end I've trailed my smart charger out under the front door and left it there trickle charging in disgrace.

 

Assuming that I've fixed nothing, which seems very likely, anyone got any further suggestions? Would it be worth investing in a VCDS lead (or whatever it is) to try and see if that'll give me any clues? It looks as if tomorrow will be spent replacing the front brake pads on my Mondeo as I need a 5 seater car for our trip to Man U on Saturday. It's times like this I regret not just having one or two decent cars like normal people, TBH.

[Lacquer Peel]

Simple code readers like this one will give you a clue if it's logged any error codes, it erases them too.

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F142752506291

[Shirley Knott]

The intercooler area was particularly covered in loads of wet looking oil though, so I do wonder if there is a leak somewhere round there.

 

 

^They all look like that around that bit of intercooler pipework IME.

 

I've had a couple of PD130 Passats (AWX) and they've both been like that, awful as it looks that's not necessarily indicative of anything sinister.

[Rave]

Hmm. The smart charger managed to get enough into the battery in 2 hours that it started without complaint. I think somebody might have left one of the interior lights on. I've just been for a test drive and it went a lot better than I expected. On the way to Lidl I found that there's still some clag when you boot it, but it's 4 Celsius according to the dash warning light and the engine hadn't made it round to the middle of the temperature gauge. I was all set to take it for a quick spin down to the nearest bit of 70mph A-road when I remembered that I'd left the back section of the undertray loose, and I soon discovered that it was dragging along under the car, so that scotched that plan. I will give it a go tomorrow once I've reattached it (or more likely ripped it off for good, as most of the fasteners are missing). I've not driven it in anger for some time so have forgotten how well it used to go, but it certainly seemed to go like a scalded cat from about 3000 rpm upwards, it span the (admittedly old, nearly bald, and summer compound) tyres up in second on the Catford one way system, so I reckon it is boosting properly. Whether it will hold the boost up a hill in fifth is another matter, I guess. We will see!

 

 

Simple code readers like this one will give you a clue if it's logged any error codes, it erases them too.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F142752506291

 

Thanks- is that going to find codes that a knockoff ELM327 and Torque on my Android phone won't? I fancied the VCDS (?) cable as if/when I do get it running properly I'd quite like to experiment with a cheeky homebrew remap for the lols- and if I could eke a few more MPG out of it that would be handy given its main job is doing long football trips...

[Lacquer Peel]

No it doesn't do anything beyond reading and clearing fault codes, I just assumed you had no way to read or clear fault codes at all.

 

For flashing the ECU you need an MPPS cable like this

 

https://www.ebay.co.uk/itm/MPPS-V13-02-Interface-Car-VAG-USB-Cable-OBD2-FOR-VW-AUDI-BMW-Citroen-Ecu-Flasher/253599751629?hash=item3b0bb91dcd

[Rave]

Ah spot on, cheers! Depending on the results of tomorrow's test burn up I may well get one of those, worth a punt for a tenner.

 

The ELM327 and Torque threw up no fault codes despite it clearly not running properly, so I wondered if something more VAG specific would be in order- but the engine management light didn't come on either, which you'd think it would if it thought there was a fault.

[Dave_Q]

Sometimes it can store a code without putting the light on, but it may not be flagging a code as the boost or airflow or whatever it is thats not right has to be outside certain thresholds to count as a fault.

 

The MPPS cable won't read fault codes, the £5 VCDS cable off ebay will be fine with the free trial version of the software.

 

Just watch for China based sellers claiming they're in the UK as they take weeks to turn up for a saving of 12p over one that will turn up the next day.

 

Finally, don't use any discs or software that come with the cable as its normally riddled with digital syphilis.

[Rave]

Well, the test drive was a mixed bag. It seems to drive pretty well, I didn't notice any obvious rattling, and nor were there any really obvious big clouds of smoke. But on the other hand, it still seems to slightly surge and falter on part throttle, and the cruise control seems to struggle to maintain a constant speed as the road heads uphill and it has to apply more power. There's still the odd puff of clag at certain times.

 

It still claims to be 4 celsius outside and I did notice that the temp gauge was often sat at less than 90 degrees- it got there under load, but fell back a bit cruising down the 40 limit sections of the A20. Up till now it's been rock solid in the middle. Is that normal?

 

My best guess as to what's happening is: that the turbo variable vanes are still sticky, I've probably freed them off a bit with my waggling them up and down, but at part throttle it struggles to set the boost level accurately, and smokes and surges a bit. Would that make sense? I'm reasonably confident that it's not going to catastrophically shit itself now so I'll take it to Manchester on Saturday- even if it only manages 45mpg that's still cheaper than 35mpg in the petrol Mondeo, despite the 10p difference in price per gallon at the moment. At some point I will try and get the EGR pipe off the manifold and shove some foaming oven cleaner down there to see if I that makes any difference. It looks like a bit of a faff though.

 

Thanks all for the help and advice so far, it has been much appreciated .

[spartacus]

I think I've seen it mentioned previously but if you can get to the turbo to spray some Mr Muscle oven cleaner on it that may sort it. My ex wife has a Toyota Previa 2.0 d4d and they're known for suffering clogged up VNT's, I cleaned it out and it's been fine ever since, that was about 20,000 miles ago.

[bigfella2]

While you were having a poke about under the bonnet did you have a look at all the little rubber vacuum tubes or whatever there called. They can cause all kinds of bother if they get damaged. Don't know if it's been mentioned before.

[Rave]

While you were having a poke about under the bonnet did you have a look at all the little rubber vacuum tubes or whatever there called. They can cause all kinds of bother if they get damaged. Don't know if it's been mentioned before.

 

They appear to be OK. I pulled the one off the top of the turbo vane actuator and it came off very easily, but then I suppose in operation the vacuum is supposed to hold it on! I might bung a zip tie round it just in case, that can't hurt.

[bigfella2]

Am not really clued up on Passat's, is there a valve block, a fag packet sized black plastic thing with other tubes coming out, and one to the actuator for the turbo like you mention. Have you had a look at the other tubes for damage?

[Rave]

I don't know, but I'll have a look tomorrow. I don't think there's any major leak (wouldn't it affect the brakes?) but worth checking. Thanks!

[Rave]

Right another update. The car was alright when I set off for my trip to Manchester but seemed to get worse as the trip went on. It wasn't obviously blowing smoke on the way up, but in the dark on the way home it became obvious when looking in the mirror with the following car's headlights to light things up that it was smoking pretty badly. The cruise control got pretty unhappy trying to maintain a constant speed up the steeper hills, surging away, though if you knocked it off and just kept your foot down it would then proceed OK, albeit with a high frequency rattle noise and smoke accompaniment. When I left the motorway, the clouds of smoke pulling away from lights or roundabouts were a bit embarrassing really- though there were 5 of us on board, two of whom are pretty big, so it was heavily loaded. MPG on both legs was about 50, whereas it was doing at least 58 on similar trips before.

 

So today I stuck it up on the ramps and whipped the undertray off again. Got that down to a reasonably fine art now. The bottom end of the hose coming out of the turbo had come about 6mm out of its socket, and the clip seemed to click when I shoved it back in again, so the metal end is clearly worn. There was oil behind the seals on the short fat hose on the other side, and I figure if oil can get past them, air can too. For some reason I'd not spaced those seals out with PTFE tape like I had the others, so I did that. Then I figured an investment of 50p's worth of Lidl's finest cable ties was worth attempting a bodge with:

 

 

 

I've taken it for a test run round the local streets again, and it seems much as it was after my first attempted fix- no smoke on pulling away, but a cloud if you boot it. This time I had my OBD reader plugged in and set Torque up to give me a graph readout of boost pressure. It's a bit hard to keep an eye on while driving, but it handily draws a circle round the top of the graph and gives you a peak pressure reading- on my final run up the road it claimed that was 20psi, which seems a lot? About 1.4 bar, or presumably around 2400mbar absolute pressure? That's higher than the target figure in Dave's GLF PD remapping thread. I guess that could be caused by the VNT nozzles being sticky? I have yet to attempt any removal of the EGR bits as it looks like a right pig of a job .

[Dave_Q]

Yes that is a bit high for a stock car. 

 

It could be caused by sticking, if you think of the turbo as having a high and a low boost position it normally starts off in the high position at low engine speed and backs off to the low position as you speed up.

 

The actuator spring defaults to the low boost position for safety with no vacuum applied. 

 

If the mechanism is totally stuck you either get stuck in the low boost position, where it will be flat until 2500rpm or so then it will feel like the turbo is suddenly working, or stuck in the high boost position where it will drive fine low down but trigger fault codes and limp mode at higher engine speeds.

 

Sounds like yours may only sticking intermittently?

 

Definitely still worth trying mr muscle if you can figure out a way to get it in, also if you go out for another test drive try logging requested boost as well as actual, actual should track requested fairly closely obviously and if there are areas where it doesn't and they match with smoke or other issues then you're on the right track.

[Rave]

Yeah I'm more or less convinced I've got sticky VNT nozzles now. The lever is basically impossible to move with your fingers- or at least it is with my bony digits in this cold weather, I reach my pain tolerance level before I run out of absolute force capability. I had thought that that might be because of the return spring being quite strong, to overcome the force from the exhaust gases acting on the vanes, but in all the videos on youtube people seem to be waggling them about with their fingers no trouble. Just found a video where the guy got the Mr Muscle in by just removing the exhaust pipe and squirting it in past the turbine wheel, so I'll give that a go tomorrow .

[Jazoli]

Yeah I'm more or less convinced I've got sticky VNT nozzles now. The lever is basically impossible to move with your fingers- or at least it is with my bony digits in this cold weather, I reach my pain tolerance level before I run out of absolute force capability. I had thought that that might be because of the return spring being quite strong, to overcome the force from the exhaust gases acting on the vanes, but in all the videos on youtube people seem to be waggling them about with their fingers no trouble. Just found a video where the guy got the Mr Muscle in by just removing the exhaust pipe and squirting it in past the turbine wheel, so I'll give that a go tomorrow .

Thats the easy way to do it and it only takes half an hour to do, it might work or might not but it's worth a try.

[spartacus]

That's the method I used, as recommended by the makers of the stuff I used. It worked.

[shedenvy]

I went in with a length of silicon hose through the egr flange on the exhaust manifold as per Laquer Peels recent post in News 24 thread. Buy some thick steel blanking plates off ebay to completely eliminate the egr pipe once you've finished with Mr Muscle. Cleaning is only a temporary fix and you'll probably need to do it again at some point. The blanking plate will make it much easier second time round.

Also the VNT actuator is hard to push against but it should be possible with a thick glove on using your thumb. Try actuating it with the Mr Muscle in there and you might feel it getting easier. I left it a good hour before bolting all the bits back togther and going for a drive. Went like shit of a shiny shovel then.

[Rave]

I am beginning to develop a profound dislike for the engineers who designed the Passat.

 

The exhaust flexi is mounted to the turbo with 3 studs. One is mounted a sensible distance from the pipe; a 2' breaker bar went on that one from above and cracked the nut loose easily enough.

 

The second one is over to the left. After a lot of faffing with it trying to get the breaker on to no avail, I eventually figured that if I removed the airbox lid I'd be able to get some leverage on it with a 12mm spanner. After pulling the fucker hard enough to rock the engine on its mounts, it eventually came loose with a bang, and I picked up a nice little cut from the engine cover mounting stud on the way past.

 

It quickly became apparent that the third one wasn't going to come undone from the top unless I removed the turbo oil feed pipe, which I didn't fancy. In any case I dropped my spanner finding that out and couldn't even see it let alone get to it with my magnetic retriever, so it was up on the ramps and off with undertray AGAIN. From underneath it was easy enough to get the spanner on it and I managed to apply enough force that I'm pretty sure my hand will be all bruised tomorrow, but it wasn't moving. I then thought I'd try twatting the spanner with a lump hammer, but even getting it in there proved a challenge, there was absolutely no chance of getting enough swing on it to hit the spanner with any force.

 

So then I figured I'd give that up as a bad job and see about getting the EGR pipe off the exhaust mani and going in from that side. The nuts at the bottom came off easily enough, but the pipe turned out not to be flexible in any meaningful way despite having some sort of flexi-looking arrangement in the middle. So then I investigated taking the whole EGR setup off the inlet manifold, only to find yet another inaccessible bolt, so I gave that up as a bad job too.

 

In the end, some further trial and error revealed that a 3/8" / 12mm socket attached to a flexi drive would go on the last exhaust pipe nut, so I got under the car one last time and eventually, working only by feel of course, managed to get that combo attached to my little 8" long 3/8" breaker bar, and more in hope than expectation gave it another massive heave. Amazingly enough, it cracked off. After yet another trip out from under the car to get a 3/8" ratchet, the three nuts are now off. At least the exhaust pipe came off easily, it's actually held on to the turbo under some tension, so was keen enough to come loose.

 

Anyway by that point I was thoroughly fed up and the first lot of Europa League games were starting so rather than start squirting caustic soda about I've packed everything up and left it. Hopefully I'll be able to get out of bed at a sensible time tomorrow and get on with it before I have to head out in the afternoon.

[Rave]

I finally did the squirting Mr Muscle in part of the job yesterday. Even that was a bit of a buggerance as the braided wire bit of the exhaust flexi is coming apart, and consequently much pricking of hands and tearing of nitrile goves ensued. Anyway I did a few squirts, followed each time by climbing under the car and wanging the VNT lever up and down from below. TBH it felt pretty good the first time, and was certainly moving pretty freely by the end. At least the foam went in looking nice and white and came out looking brown and grotty.

 

On the subsequent test drive the bloody thing was still surging a bit and seemed pretty keen to spike the boost up high when the throttle was floored. I was going to take it for a quick wang down the dual carriageway bit of the South Circular but one look at the queue to get onto it put me off that idea. In the end I took it to my favourite empty car park and did a couple of full bore runs from one side to the other in second. On the first run the boost spiked at a fairly impressive 22.5 psi, but on all the subsequent ones it peaked at 16.5. Having discovered that it was still blowing impressive clouds of clag when I booted it away from a following car on the way home again I figured that the first run had blown one of the boost pipes off again, but they looked pretty secure when I climbed underneath.

 

I'll just have to see how it goes on our run up to Yorkshire on Wednesday, I guess. I might buy the VCDS cable and try logging requested boost against actual boost, and I might see about replacing the vacuum pipe to the actuator, which does look pretty aged.

[bigfella2]

I think they run about 19psi as standard, 22psi is a bit of a boost spike, but as long as it doesn't stay at that your fine unless it's been mapped. Is the intercooler damaged in anyway, still think there is a boost leak, is there a whistling noise come from the engine when driving, don't rev the engine to listen to it as a pd won't make boost unless its under load.

[Rave]

There's not been a whistling noise, more a high frequency rattling like, I don't know, gently poking a piece of wooden dowel into a moving alloy wheel would sound. Not sure how better to describe it really. But it's the kind of noise that pulses of air blowing past the metal end of a boost pipe could make, anyway.

 

I think there was a boost leak from at least one of the pipes, and I'm hopeful that my cable tie bodge is now holding them on properly. And because the car is still misbehaving, I think the boost leaks are a symptom of another problem (causing boost spikes), not the cause.

 

I'll have a better idea how it's behaving after our trip to Yorkshire on Wednesday in any case . I'll leave the ELM327 plugged in and keep an eye on things on the way.

 

Where is the sensor that measures the boost level anyway? You'd think they'd put it close to the inlet manifold so that any leaks between the turbo and there would be apparent?

 

Edit to say: I am increasingly thinking that the vacuum pipe to the actuator could be at fault for fluctuating boost levels, as I don't think the vanes are sticky any more, if they ever were. Fluctuating boost levels could in turn cause the surging effect. I'm not sure that an ELM327 and Torque have enough granularity to show me if that's happening, but we'll see. Presumably replacing that length of pipe won't be any more of an arseache than the various other things I've attempted so far, though I daresay there'll be some way in which VW have made it a much harder job than it should be.

[bigfella2]

On the Ibiza pd130 it's on the intercooler maybe the Passat is the same??

[Rave]

The Passat continues to a ) work, albeit using 20% more fuel than it should and b ) confuse and annoy. It got to Yorkshire and back OK, and was a fair bit less smoky in normal driving, so I think that my cable tying some of the boost pipes on has had some effect. I had Torque running on my phone showing boost pressure, and the surging effect on medium throttle openings was indeed accompanied by fluctuating boost levels on the graph.

 

I did a bit more googling to see about changing the vacuum hose to the turbo actuator, and eventually found this useful site:

 

https://sites.google.com/site/1810martin/home/b5-vnt-turbo-problems

 

From there I learned that, somewhat counter-intuitively (to me at least), the turbo's default position is to have the vanes 'open', so not providing any boost at low speed / much restriction at high speed. When you start the car the actuator pulls the vanes closed. From there on, the boost is regulated by reducing the amount of vacuum to the actuator so it relaxes and allows the vanes to open up again. And when I tried today, sure enough the actuator was pulling the vanes on startup, releasing them when you pull the pipe off, and then pulling them back up when you put it back. 

 

I then pulled the MAP sensor out (it's on the pipe that goes across behind the engine) and stared at it for a bit, before reinstalling it. Then I decided to try and loosen that pipe from the inlet manifold so I could have a stare in to the EGR gubbins. Unfortunately it  has all sorts of stuff bolted to it and I couldn't move it very far at all. I put a bit of teflon tape under the seal and then tried reinstalling it with cable ties holding it in place. I did the other end as well.

 

Then I set off to drive to Lidl to buy some half price cookies. It quickly became apparent that the car now had little or no boost. It was nice and smooth to drive, no surging or high frequency rattling, but didn't have much get up and go. I found that booting it in second would eventually get it to boost up to about 8psi, once it was past maybe 2500rpm, at which point it blew a cloud of black smoke.

 

When I had yet another look under the bonnet, it didn't take me long to find out why- waggling the inlet pipe about had pulled a vacuum pipe that runs along it loose; the hissing/sucking noise was quite obvious. I pushed it back in, and the VNT actuator started moving again. Then I gave the MAP sensor a quick squirt of the brake cleaner that I'd collected from my mum's on the way back from Lidl. Not much dirt came out. On yet another test run it seemed to be exactly as it was before, still with the rattly noise, maybe not as much surging. A final look under the bonnet afterwards revealed that the pipes had moved out from their sockets despite the cable tie action, so I've nipped them up really tight now.

 

Despite all of this irritation, the car has never thrown an overboost fault code or gone into limp mode. If the MAP is working properly, then it's seeing fairly high levels of boost 3/4 of the way round the inlet system, after the intercooler etc. One thing I have yet to try, per that helpful page linked above, is the bleed pipe from the N75 valve to the airbox; I guess if that's blocked it would stop the actuator backing off the turbo vanes as much as it should. The high fuel consumption on a motorway cruise, without any particularly obvious smoke, might just possibly be caused by the turbo severely restricting the exhaust flow and thus increasing the load on the engine. But I'm not hopeful.

 

I'm going to order that VCDS lead I reckon, it's cheap enough and might be useful. If that doesn't work then I guess investigating the EGR system will be next. I'm off to France in it tomorrow as my father-in-law has been hassling me for ages to take him on a booze cruise. With any luck some gillets jaunes will set the fucker on fire .

[Rave]

The Passat's MOT ran out on 22nd December last year. On that day it got me back from a fairly memorable trip to Manchester at 5 minutes to midnight and has been sat on the drive ever since. However I now need the drive to get some of my other MOT-less cars off the road, as their tax is about to expire, so I've spent the last couple of days finally fitting the new front shocks, which turned out to be nothing like as easy as the Autodoc video made it look. I ended up spending £150 on a spring compressor station from Machine Mart after cocking about for hours trying to get the springs wound down with my old pair of hooks-on-a-threaded-bar type compressors without success. However I got it done in the end, no thanks to whoever designed it. The top nuts are hidden under a pair of plastic covers, which appear to be bonded in place with sikaflex type mastic before the car is even painted as far as I can see- I mean what the fuck is that about? And on the O/S one is hidden under the air con pipes, on the N/S it's under the fuel pipes. I daresay on a pov-spec petrol it'd be fine, but it was a complete bugger on this. I suppose it's impressive that it got to 244k miles on the original dampers.

And so having fettled a couple of other minor things I took it up to the MOT station this afternoon, via a very circuitous route to get the cat etc. nice and hot. I wasn't hopeful as it's still smoking like a bastard as soon as you get any boost on over 2k RPM, but the MOT station didn't even test the emissions, and didn't care about the cloud of clag it emitted when they revved it up to get it onto and off the brake rollers. So I now, amazingly enough, have another road legal car, that's 4 now.

So I'd obviously like to try and get it running properly, in which case I'll treat it to a set of new tyres and press it into service as next season's football away day bus. But I'm running out of ideas. I carefully read through everything on the list in the link in the post above, and this is where I am now:

• Turbo vanes cleaned with Mr Muscle and moving freely as far as I can tell. Certainly the actuator moves the lever up when you start the engine and down again when you switch off.
• All pipes between turbo and inlet manifold (there are many) bound in place with zip ties. No obvious holes in any of them.
• EGR valve removed and checked. It is not stuck open and opens a few MM when you poke it from below, albeit it takes a lot of force to move. It was pretty dirty, but not really enough that it would badly restrict airflow through it. Anti-shudder valve butterfly moves easily.

Things I have yet to try:

• Disconnecting EGR vacuum hose and plugging it- worth a go, I suppose.
• Fitting a new MAP sensor- it occurs to me that it is possible that it has gone wrong and is reporting too high a boost level, causing the ECU to over-fuel. However I'm not sure why that would cause the engine to surge under moderate loads, while reporting corresponding boost fluctuations via the OBD port- unless, I suppose, the ECU is adjusting the fuelling in real time in response to the varying boost signal, which I guess would (fairly obviously) cause noticeable surging?
• I have also yet to check that the bleed valve from the turbo boost controller to the airbox is clear, though I'm expecting it to be.

Anyone got any more suggestions? I have yet to try my VCDS cable, anything obvious to check if/when I do?