Engine revs high on BMW 4 pot

[Vince70]

Hi I've got a bit of a problem with both my Z3 and my E36 which both have the M44 twin cam 4 pot engines in that the revs seem to stick at around a 1000 rpm and then a couple of seconds later the revs will drop to about 800 rpm rather than just dropping to 750 rpm straight away but both cars seem to rev ok...

 

It's quite frustrating especially when sitting in stop start traffic and I can't find any noticeable air leaks on either car and wondered if anyone had experience of this problem and could give me a few pointers...

[purplebargeken]

Idle control valve?

[mitsisigma01]

Hi , I have a similar problem on my mitsubishi sigma 3.0 estate , my problem made worse by the fact it is the only 1996 one left on the road in the UK .

I have checked and cleaned for air leaks then the MAF , then the EGR valve , then the TPS , sometimes she is spot on sweet as a nut other times she pulses like a mad bitch between 1k and 3k revs , then when dipping the clutch at a junction she stills but not always but does immediately restart but doesn't necessarily do what she was doing before the stall .

Being the last one on the road (unless someone knows differnt )

Trying to find info on the mad bitch is impossible .

I used to be on a bmw forum and there was plenty of helpers and info on there , but finding the source of yours could be a shitter or simples ! Good luck !

[scaryoldcortina]

Sticky PCV valve? I've fixed a few 4 pot BMW engines after other places already tried ISCV/MAF and VANOS replacement by cleaning this (it's a bitch to get at though). Basically acts as a huge unmetered air leak because BMW engineered* the crankcase return into the manifold after the throttle flap.

[Stanky]

Are the TBs controlled by a physical wire from the accelerator or by electrical wizardry? If its the former then try loosening the throttle cable a bit. I had the opposite problem with the Kia we used to have and sorted out its general bogginess by upping the idle from ~600rpm to ~1000rpm before we sold it.

 

Its someone else's problem now, but might be worth a look? Bascially slacken it of a bit.

 

If its electonic with a stepper motor then I can be of no help whatsoever.

[Pete-M]

Coolant temp sensor.

[Noel Tidybeard]

is this the emissions thing thst injected car do since the 90's- first car i found this on was a twink granada

 

seemingly if throttle snaps shut nuns & kittens can be harmed by OMGUNBURNTFUEL- so the pause in revs allows more complete burnage ergo safe n & k

[320touring]

Shonky idle is likely either the idle control valve (pull it off and pap some carb cleaner through it) or its a sticking cable/throttle body.

 

Have you italian tuned them both?

[Vince70]

Thanks for the help I did clean up the idle control valve today on the E36 as it seems more of a problem than on the Z3 and it didn't make much difference..

But I noticed the car had a very rough loud sounding exhaust when I got out the car and put my hand over the end of the exhaust and noticed that although the exhaust is relatively newish item it had a couple of holes in both of boxes but in the last 3 years it's only done about 750 miles and I've done 700 of them in the last couple of months so I guess that's the reason it's rotted out so I ordered this..

http://www.ebay.co.uk/ulk/itm/181376825994

I ordered the same make one for my Z3 and these exhausts are great quality and the bargain of the century so I'm hoping it will help with the idle problems..

But I've got to admit I don't really drive the cars much and rarely drive over 4000 rpm so I might have to give both cars a bit of an Italian tuneup...

[Vince70]

I bought a second hand idle control valve for £10 with free delivery off eBay and also treated it to a couple of nice stainless steel Allen key bolts rather than those horrible torx head things the other day as it still wouldn't idle below 900rpm on the old idle control valve even after cleaning it out with a bit of carb cleaner but it was a lot better than before and wasn't running lumpy.

 

I also sprayed the throttle housing and the new valve with a good dose of carb cleaner before fitting It and it's now running great and ticks over at around 780rpm..

Thanks for the help.

[Vince70]

I still have the idle problem with the car revving too high (1100 rpm on average) and have now cleaned out the idle control valve and also I tried disconnecting the MAF but that also didn't make any difference so the next step is to buy a throttle position sensor so it's fingers crossed that sorts out the problem as the car is getting horrible to drive in stop start traffic..

But it does rev nice a free now but every time I change gear I get a surge and I can't find any air leaks..

 

I do have the bmw software disks indoors with the fault reading software but it's easier said than done to get it to install on poxy Windows 10 as it sees it as a virus and I can't fully get the virus protection turned off so bring back XP lol.

[Cavcraft]

My old E46 323 6 pot used to sort of stick slightly when you were giving it some welly, the revs took a while to drop.

[Luxxo Waftybarger]

The throttle butterfly valve gets gummed up with carbon deposits which stop it returning properly. Might eXplain it. My e46 318i needed it cleaning a couple of times. They also rev high for a couple of minutes when you first start then from cold, that's normal.

[Christine]

My audi 80 did it , anti stall apparantly , right  bitch in traffic .Mechanic said they all do it, but if it had been new I'd have sent it back .Never did cure it .You'd go to creep forward and the engine would surge up to 1500 and then 2 or 3 seconds to return to idle, bastard thing !

[Vince70]

I took the throttle body off yesterday on the E36 and gave it a good soaking in some carb cleaner and polished the innards with some autosol and also gave the idle control valve another good clean while I was at it..

 

I also disconnected the throttle cable and ran the engine without it connected and when the car revs up the revs seem to still stick at around 1000 to 1200 rpm but at least I now know it's not that.

 

I do have a throttle position sensor on order so I'm hoping that will cure the issue and I might have a play with the throttle position screw to see if I can someway sort the problem..

 

It didn't help yesterday taking the z3 out for a spin as its mechanically the same car and drives so much better without the sticky revs issue.

 

But this morning I decided to just run the car without the electrical connector fixed to the idle control valve and its ticking over lovely but it sounds Like there's an air leak in the system when I do that but when I reconnect the sensor the noise disappears but the revs increase by another 2/3000 rpm.

[Vince70]

I think I might of made a bit of progress as I put the old idle control valve back on the car and it was still as bad as ever but decided to take the new/old one apart as I had nothing to lose, so I drilled out the retaining pin on it to find that when apart it was rusted up something terrible which reduced the free movement of the valve and I could of soaked it in a gallon of carb cleaner all day long and it wouldn't of made any difference, so I've now cleaned it up and the valve will now work properly hopefully..

 

So it's now ready to go back on yet again but now that its been on and off so much the gasket has finally given up the ghost so I've ordered a new one from bmw which cost at least a quid lol

 

I could of bought a new valve on eBay I guess for just under £30 I found out afterwards but that's a cheapo pattern part which will most probably last all of a week and the original Bosch units are anywhere between £140 to £200.

http://www.ebay.co.uk/ulk/itm/281571132316

 

so now that I've repaired one valve I'm going to do the other one so I have a spare for both motors.

[Vince70]

Well I've just diagnosed it isn't the idc valve as it was still ticking over at about 1400 rpm so just to make sure it wasn't defective I took a good working one one off the Z3 and tried that in the E36 and it was still doing the same thing..

 

The thing is if I leave it disconnected it ticks over and runs lovely so I'm completely baffled to the reason why it's revving it's nuts off.

[Vince70]

I just wanted to say a big big thank you to scaryoldcortina for the advice on the PCV valve thing as now the car runs fantastic after cleaning it out with a bit of carb cleaner..

 

I had to look up in the net to find out what it looked like and I think the worst part of the job was droping my ratchet and socket down into the depths of the engine bay and having to remove the battery tray and dislocate my arm to retrieve the part but it made taking the part off easier anyway..

 

At least I now know the car is 100% as it's got a nice clean idle control valve and I even polished the innards of the throttle body..

 

I've still got to put the gasket back on when it arrives but the car is now running better than ever.

Thanks for the help.