405 doesn't want to drive

[carlo]

Would be very grateful if anyone has any other advice on trying to get my daily back on the road.

 

For a month now it won't idle properly; either cuts out as soon as you take your foot off the throttle, or may work sometimes but then cuts out after a few minutes.  You also get a 'surging, engine braking' sensation when driving, although under load it seems fine and accelerates without issue.

 

I thought I would be able to fix this myself, the last time it did something similar I discovered an air pipe to the MAP sensor was half hanging off; re-connected it and all was A1 again.  This time, despite the same pipe looking a bit loose it made no difference when I secured it.  Have replaced the idle air control valve, checked all pipes for leaks, and even replaced the whole throttle body with another working one to no avail, still cuts out and has added a symptom of rev surging between 800 - 1500 revs too.  I think I may have changed too many bits now and probably gone backwards.  My mechanic is not sure what to do next, suggested I let a garage loose on it.  He's suggested it might be the fuel pump sender unit above the tank starting to fail, well I have a spare so could try that.  Or possibly crank sensor??  He doesn't see to think it's anything to do with plugs/leads as it starts fine and works on all 4 cylinders.

 

This is the worst issue I've had with it in four years.  Bollox.

 

 

 

[Crispian_J_Hotson]

You got an afm on it? If so, check it's sweeping correctly and within its operating parameters. 

[The Reverend Bluejeans]

Considering how much these are worth now, I'd fire it into a main dealer.

 

'Fix it my good man'.

 

 

[Junkman]

You got an afm on it? If so, check it's sweeping correctly and within its operating parameters.

A fucking what???

[The Reverend Bluejeans]

Airflow meter. The metal things with the hinged flap before plastic hot film MAF's.

[carlo]

Is an afm a mass air flow meter?  And no I don't know if it has one!  Probably too old.

[The Reverend Bluejeans]

Air flow meter (AFM) - metal and has a hinged flap. As used on Bosch L Jetronic as well as older Motronic. The act of air entering the engine opens the plat and the potentiometer on the flap tells the ECU how much fuel to inject. 205GTi's had these.

 

MAF - Mass Air Flow. This is a heated element in a plastic tube and the air flowing over it tells the ECU how much fuel to inject.

[Crispian_J_Hotson]

Yes. When they wear out they will skip over the potentiometer track at any point causing misinformation to the ECU, either sporadic or no information which will make the engine run like a bag of shite at any given range. Often it will give symptoms of other sensors like the coolant sensor having failed so one can end up changing every part of the injection system without rectifying the issue. 

A simple reading test on an ohm meter can show if it's operating correctly, there is lots of information on the web and afm's were used by lots of manufacturers, wear can be adjusted out sometimes too.

Really need to get to grips with testing the injection system and its characteristics first though as it will be expensive changing out random parts. It's not as hard as it makes out.

[2MB]

Only petrol Pug I had had a carb so I can’t be of any help but it’s a lovely looking thing and looks well worth sorting

[willswitchengage]

Is there 50p stuck in the handbrake?

[Jim Bell]

Is there 50p stuck in the handbrake?

Hooray!

 

Its been so long.

[robinmasters]

Is there 50p stuck in the handbrake?

Looks like there might be one shorting the front fog light wiring.

[carlo]

Hurrah!!

 

After a week of faffing around and getting nowhere, and more disillusioned, looks like I might have cracked it.  Simply disconnecting the battery, which presumably resets the ECU, seems to have done the trick.  Idles perfectly, no cutting out and no surging after a half an hour's drive this evening.  Fingers crossed eh  -  had horrible visions of having to but something more modern.