E34 M50 2.0 Manual - Irratic idling

[Cressidom]

Good day all,

had completed an overhaul about a month ago on my M50 2.0.


Irratic idling still exists. Trouble shooting started with the following done.


New Cyl head (was cracked)

Changed Throttle Body...

Changed AIr Mass..

Changed Coil pack rubber suppressors...

Engine balanced / lightened with single mass flywheel.


PRoblem is hard / long starting..and hesitation etc.


Any ideas or feedback appreciated.



Cheers

Dom

[bmwrp8]

try checking fuel pressure

[whiskychaser]

Checked intake hoses/manifold for air leaks?

[Morgenster]

Doesn't a lighter flywheel make for a lumpy idle?
What exactly are the symptoms?

[Ferret]

Doesn't a lighter flywheel make for a lumpy idle?
What exactly are the symptoms?

I wouldnt have thought it wouldnt cause too much change in idle on a 6-cyl...

Check for vaccuum leaks!

With a lumpy idle it's almost always:

Check! Check! Check! Check! *Find vaccuum leak that you swore blind wasnt there on the last four checks!*

[Dr. evil]

clean idle control valve

[Morgenster]

I wouldnt have thought it wouldnt cause too much change in idle on a 6-cyl...

Check for vaccuum leaks!

With a lumpy idle it's almost always:

Check! Check! Check! Check! *Find vaccuum leak that you swore blind wasnt there on the last four checks!*

I agree but that's when you look at a perfectly tuned engine with six injectors, valves and coils all clean and working exactly the same. My reasoning is that if there's anything out of tolerance there it'll be much more noticeable with a lighter flywheel which would compensate for this.

Besides, what's erratic idle? too low, too high RPM? rumbling, shaking, missing? Cold or warm? does it appear at certain times or is it always there?

Anyway, the hesitation part is an indicator for vacuum leakage or faulty sensors other than the MAF.

[Cressidom]

Hi all...

thanks for all the info...The engine was p & p'd / balanced/ incl the flywheel and pressure plate. When I stomp on the pedal..there's hesitation..most times..and sometimes..it works fine..on cold start up it idles fine. Then as it get hot sometimes yes sometimes no.

When I had the manifold out I checkd the manifold myself for cracks.None was found,I will sweep the hoses again. HOWEVER...there's a form of 'hissing' that was coming in from the glove compt.(bear in mind RHD) When I took out the GC..found the cabin temp sensors. Plugged the vacumm for that and when I accelerate...nothing when the RPM drops...i hear the hiss..air.

Read somewhere that Pulley sensor or cam sensor can also cause similiar probs.MAF was swapped from a donor car (which ran fine) but on mine still presisted. My other options are to change all coil packs..pulley & cam sensor.

Anymore feedback appreciated.

Dom

[Ferret]

on cold start up it idles fine. Then as it get hot sometimes yes sometimes no.

...there's a form of 'hissing' that was coming in from the glove compt.

Classic signs of a vaccuum leak... There may be something so glaringly obvious that you've overlooked it, take a step back and check everything's screwed into the manifold tight and all the little annoying hoses that run under the manifold are plugged up tight.

The 525i I had of that age, all of it's vaccuum hoses were disintegrating by now...

[whiskychaser]

Hi all...
Read somewhere that Pulley sensor or cam sensor can also cause similiar probs.MAF was swapped from a donor car (which ran fine) but on mine still presisted. My other options are to change all coil packs..pulley & cam sensor.
Dom

Sure I read you can check for vacuum leaks by squirting WD40 around the suspect area -the idle changes momentarily. If you really really cant find one why not check for fault codes -You can go on replacing bits for ever