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:)

[Cressidom]

hi whisky...thanks for the tip on the WD40.

Will try that...

OHHH one more thing I forgot to mention....sometimes when I start it hot..I.e. in the mid high temps...Get a pooping sound..like vacumm in blowing in reverse..and have had a couple of times...had hoses pop out from thier connection...the last time..the one from my fuel regulator popped out.

Cheers
Dom

[whiskychaser]

...had hoses pop out from thier connection...the last time..the one from my fuel regulator popped out.
Dom
The hoses need to be airtight. Use insulation tape if need be just for now. The little insignificant looking one from under the manifold to the regulator helps control the mixture.

[Morgenster]

hi whisky...thanks for the tip on the WD40.

Will try that...

OHHH one more thing I forgot to mention....sometimes when I start it hot..I.e. in the mid high temps...Get a pooping sound..like vacumm in blowing in reverse..and have had a couple of times...had hoses pop out from thier connection...the last time..the one from my fuel regulator popped out.

Cheers
Dom

What do you mean? The engine farts?? or is it more like a bang?

[Ferret]

What do you mean? The engine farts?? or is it more like a bang?

This sounds more like an intake backfire, wonder if the cam chain's slipped or something.

[Morgenster]

This sounds more like an intake backfire, wonder if the cam chain's slipped or something.

Yep, that's what I was thinking too, at least if the sound is a bang. There's no way you can get an intakebackfire if the valve timing is good on an m50.

[Ferret]

Yep, that's what I was thinking too, at least if the sound is a bang. There's no way you can get an intakebackfire if the valve timing is good on an m50.

Hard starting is a direct knock on of this as well... first time I ever rebuilt an M50, I slipped the intake out by a small amount - and it was hell to get it to start - could be a stuck vanos unit if the cars fitted with vanos. I cant tell cos it wont show me profile details in reply mode.

EDIT: Now I can see his profile it's a '91, deffo not vanos.

Whip off the timing cover, put the engine at TDC and check the square lobes at the back of the cams are dead flat parallel with a steel ruler. I think your timing may be out.

Does it idle like a lawnmower and chug when you put your foot down?

[whiskychaser]

Whip off the timing cover, put the engine at TDC and check the square lobes at the back of the cams are dead flat parallel with a steel ruler. I think your timing may be out.
Does it idle like a lawnmower and chug when you put your foot down?

Agree. But I think you mean the valve cover. Hope he isnt busy taking the wrong one off.....:)

[Ferret]

Agree. But I think you mean the valve cover. Hope he isnt busy taking the wrong one off.....:)

Whoops, well spotted sir!

[Cressidom]

Hullo Gents...

thanks for all the inputs...Mine is a 91 non vanos UK spec.520 i.
When I said Popping sound - it was lime someone was punch a hole in a tire and you get that kinda of popping ? (dunno if I'm making sense).

Anyways..it does not happen all the time just 'occasionaly' very rarely now after the rebuild.Also have a (in my observation) a lot of oil in the manifold when I removed it to clean the butterfly.

The M50 Timing was set using a special tool - something that held the back of the cams flat in place when timing was set.But still an area to look at.
OH the FUEL PUMP died on me this friday morning on the way to work,Had one from the chop shop near work deliver one..(looked a whole lot better than what I had in the tank) ...Car runs better...got more power in it/improved performance...but still hesitating at times..and idling still a bit rough..

The sensation is when I tap on the throttle..and know for the fact that the Butterfly is opening up more..but no 'instant' reaction to pick up speed..
so could it be the following ?

1 ) bad TPS ?
2 ) Leak in the rubber bellow from the MAF ?
3) Other air leaks ?
4) maybe at an adjustable FPR ?
5) CAM sensor ?
6) CRANK sensor ?
7) COIL PACKS..shorting on the head ? going bad ?

IT's embarrasing as the lights turn green....I'm getting beat by 3 cylinder car.

Appreciate more feedback.

Cheers
Dom

[whiskychaser]

1 ) bad TPS ?
2 ) Leak in the rubber bellow from the MAF ?
3) Other air leaks ?
4) maybe at an adjustable FPR ?
5) CAM sensor ?
6) CRANK sensor ?
7) COIL PACKS..shorting on the head ? going bad ?
Dom

Hi Dom. I think what you need to do is eliminate things logically. We already said make sure you got not air leaks but you are listing 3 possible places above. You have to make sure you DONT have a problem with them. If you think its a duff sensor, get the fault codes read as suggested. Then maybe try substituting coils packs etc.

[flash]

Hullo Gents...
The sensation is when I tap on the throttle..and know for the fact that the Butterfly is opening up more..but no 'instant' reaction to pick up speed..
so could it be the following ?

IT's embarrasing as the lights turn green....I'm getting beat by 3 cylinder car.

Appreciate more feedback.

Cheers
Dom

Hi Dom,

My car too used to backfire occasionally upon starting. In such cases, I would invariably find one vacuum hose loose or detached. To save cost, I just zip-tied all vacuum hoses. Problem solved until the hose pops out.

I too get beaten or more like bitten by the 3 cylinder cars (Kancil, Kelisa, Kenari) at the traffic lights. Our cars are SLOTHy from standstill:D . But our cars can generally mow them down at higher speeds.

And yes, my car too takes it time to pick up speed even when I press the pedal to the metal.:( We gotta accept the fact we have a SLOTH and live with it or upgrade.:D

A M50B25 Vanos transplant is in the works provided my Minister of Finance approves the expenditure budget.:D

[Cressidom]

Hi whisky..and the rest...

will do the needful and hopefully it's nothing more painful (expensive ),
Will check for air leaks again, and then maybe the new coil test.

failing which the cam and crank sensor will need change.

Cheers
dom