Cold idle poblem

Hi guys, i have a 1994 540i, owned it for a while and since ive owned it its always had cold idle problem, ive replaced the spark plugs, mass flow sensor, fuel filters, fuel pump, fuel pressure regulator and the vacuum hose to the for.

When i first got the car its cold idle was erratic always up and down, and almost stalling, since replacing the fuel pump and for the erratic idle has sopped and it just has rough cold idle and still wants to stall but manages not to. and when its hot its perfectly fine

does anyone know where to go next, im tempted to just give to a dealer to diagnose as with me being a heavy diesel mechanic im tired of fixing stuff all week and then having to fix my own stuff at the weekends.

You may have a intake manifold gasket leak when it is cold , the reason it idles fine when it is warm is because the seal has expanded .

Sent from my Desire HD using Bimmer App

At which point on the dash thermostat does the idle normalise ? Exactly ? I may be able to help you, we had a similar issue just diagnosed last week. It was a fuel injector. Thete was no clue before that.

Perhaps you can begin with the disconnect test ? And have you pulled your error codes via the stomp test? Please google and youtube for the demos for this.


And Noel sir, there was a discussion here recently where it was shown that rubber gaskets contract when heated so i dont think that is the case.

I'm not sure how the conclusion was reached proving gaskets shrink when heated. Most engine gaskets are not rubber to begin with. The other conveniently missed point in that discussion was that the metal parts seperated by the gasket do in fact expand with engine heating, closing air leaks. This really quite common on engines, please be careful what you belive when reading here

was that the metal parts seperated by the gasket do in fact expand with engine heating, closing air leaks. This really quite common on engines, please be careful what you belive when reading here[/QUOTE]

+1

Sent from my Desire HD using Bimmer App

Originally Posted by snowsled7

I'm not sure how the conclusion was reached proving gaskets shrink when heated. Most engine gaskets are not rubber to begin with. The other conveniently missed point in that discussion was that the metal parts seperated by the gasket do in fact expand with engine heating, closing air leaks. This really quite common on engines, please be careful what you belive when reading here

That's because that discussion focused on the rubber/polymer gaskets primarily, and not on the other elements. IOW it was not an obtuse and meaningless debate. Most people who followed the arguments to and fro noticed this.

The scientific fact that rubber shrinks when heated was referred to here as Noel mentioned intake manifold gaskets, which perhaps you have forgotten is made of rubber or similar polymers. Your reference to most engine gaskets not being made of rubber, while correct, takes his reference out of context, without clearly stating this.

So yes OP (original poster) , please be careful about what you read here. It is quite common for some to distort discussions by expanding, contracting and distorting and taking arguments out of context on the sly. Fortunately, after some time, you see these patterns and learn to discount them quickly. Also fortunately, you are a mechanic by profession and probably have accounted for vacuum air leaks that might be sealed by metal expanding when heated...

Assuming that the stomp test does not reveal anything usefull, you will have to do the disconnect test first. Assuming that does not help, then please consider that it might be a fuel delivery problem, which seems to be the case because replacing the pump improved your symptoms (the older one would surely be more tired than the new, which would have exacerbated a fuel delivery issue. We just worked on a car that had the exact mysteriously displayed a FI#3 code when we disconnected the ICV. Does not show up on other identical engines when the same disconnect is done. Same consistent bad cold idle issue as yours that normalises when the engine heats up. No bloody fault codes. Purely as a coincidence, I would look there next, find a way to test that fuel delivery when cold is the problem (we will be using carb cleaner to supplement the injectors when cold), and then zero in on the problem.


rgds,
Roberto

" Properly operating fuel injectors play a major role in fuel delivery.
The Motronic ECM switches the injectors on and off at
the negative (-) or ground side of the connectors. Positive (+)
battery voltage is always present at the connectors when the
engine is running. An injector that fails or loses power will not
open, creating a lean air-fuel mixture and causing the engine to
run poorly when cold or stumble on acceleration. An injector
that shorts to ground will remain open constantly when the engine
is running, creating a rich air-fuel mixture that can dilute
engine oil, foul the spark plugs, cause a rough idle, and eventually
destroy the catalytic converter. See 130 Fuel Injection-
DME for fuel injection system troubleshooting and repair. "

Thus, a SINGLE injector can cause these problems. You don't need more. And the issues that we dealt with DID NOT generate a FI fault code under normal circumstances. It was a christmas miracle that it did when we disconnected the ICV....i still don't get how that could go together.

OP, forgot to ask you if you have downloaded a copy of this Bentley manual for E34s ? Please google for the download links. Perform a fuel enhancement test...something quick and dirty. Let us know about it. C'mon the year is coming to an end and you might nearly be there. Good luck !

Originally Posted by robertobaggio20

That's because that discussion focused on the rubber/polymer gaskets primarily, and not on the other elements. IOW it was not an obtuse and meaningless debate. Most people who followed the arguments to and fro noticed this.

Pretty sure most of us found it obtuse and meaningless

The scientific fact that rubber shrinks when heated was referred to here as Noel mentioned intake manifold gaskets, which perhaps you have forgotten is made of rubber or similar polymers. Your reference to most engine gaskets not being made of rubber, while correct, takes his reference out of context, without clearly stating this.

So I am correct but out of context?

So yes OP (original poster) , please be careful about what you read here. It is quite common for some to distort discussions by expanding, contracting and distorting and taking arguments out of context on the sly. Fortunately, after some time, you see these patterns and learn to discount them quickly. Also fortunately, you are a mechanic by profession and probably have accounted for vacuum air leaks that might be sealed by metal expanding when heated...

So as I and others have pointed out, leaks that go away when the engine warms are common problems with older vehicles, no distortion, no out of context, just a simple fact garnered through decades of EXPERIENCE

Assuming that the stomp test does not reveal anything usefull, you will have to do the disconnect test first. Assuming that does not help, then please consider that it might be a fuel delivery problem, which seems to be the case because replacing the pump improved your symptoms (the older one would surely be more tired than the new, which would have exacerbated a fuel delivery issue. We just worked on a car that had the exact mysteriously displayed a FI#3 code when we disconnected the ICV. Does not show up on other identical engines when the same disconnect is done. Same consistent bad cold idle issue as yours that normalises when the engine heats up. No bloody fault codes. Purely as a coincidence, I would look there next, find a way to test that fuel delivery when cold is the problem (we will be using carb cleaner to supplement the injectors when cold), and then zero in on the problem.

Sure sounds impressive... Do you think it will work?

Could be your IAC is sticking when it is cold, and becomes unstuck once the engine has warmed up.