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Discussion Starter · #1 ·
Arrgghhhhhhhhhhhhhhh!!!

This is never ending.

So I change the cam cover gasket and now my idle is terrible. Just to be clear, when dipping the clutch, my idle used to nicely drop to about 1100rpm, hold for a split second there, and smoothly drop to around 700rpm. Now it drops like a stone to near stalling, bounces back up to over 1000rpm, then basically bounces around and hunts.

I've dug up this thread:
http://www.bimmerforums.co.uk/forum/f17/e36-1997-323i-vacuum-leak-t2452/

which suggests the regulating valve down from the cam cover vent hose was the culprit, but I'm wondering how crank case vent pipework can interfere with the idle?

Just as a back story, I found out I had the wrong cam cover gasket after ripping the old one out. So I put the old one back on to get down to the parts shop. Now this gasket was leaking beforehand, and when put back on, was leaking even more. When I first started the car after putting the old gasket back on, the engine reved to over 2500rpm, then took over 10 seconds to pull itself down to a more normal cold idle speed of just over 1000rpm. There was smoke everywhere and the strong smell of fuel.

I drove to the parts shop and it cut out twice while dipping the clutch. After putting the new, proper gasket on, the car has started fine, and hasn't over reved, but now I get this poor idling issue. It runs pefectly off idle and through the revs.

Any suggestions on what's happened here? And what is the purpose of that regulating valve located down from the cam cover vent pipe, which solved the idling issues in the thread linked above?
 

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Sounds like an air leak to me. Did you have to remove any other pipes?

You'll need to check that the gasket at the rear of the block is seated in place correctly. Due to limited amount of clearance it is often possible to dislodge the seal at the back where the semi circular solid section sits:thumbsup
 

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Discussion Starter · #3 ·
Sounds like an air leak to me. Did you have to remove any other pipes?

You'll need to check that the gasket at the rear of the block is seated in place correctly. Due to limited amount of clearance it is often possible to dislodge the seal at the back where the semi circular solid section sits:thumbsup
The only pipe I removed was the one from the front right of the cam cover, that goes down to that regulator value and oil seperator assembly. But why should a leak in the cam cover gasket cause erratic idle?
 

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Any air leaks on a BMW cause erratic idle, hence why the idle changes when you remove the oil cap ;)

Have you rechecked your work to make sure the car doesn't leak oil and the seal is on correctly all round?
 

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Discussion Starter · #6 ·
Any air leaks on a BMW cause erratic idle, hence why the idle changes when you remove the oil cap ;)
I never knew that. So any leak around that gasket, and associated parts could be the problem? Is it possible the car has been running with a leak and since the gasket change, the leak is gone, but the car is still running on the old map or program if any such thing is possible? Maybe a battery disconnect for an hour could reset something? Or should it just relearn? Or am I talking nonsense? I'll obviously check my work first though.

What I still don't quite understand is why a leak in the oil ventilation system, including cam cover, causes erratic idle. Obviously its directly seperated from the inlet vacuum area, where a leak very obviously causes idle issues. I'm sure I remember something about oil vapour needing to be recirculated through newer engines because it can no longer be vented to atmosphere (environmental regs some time ago), so perhaps that regulator on the oil seperator allows the vapour from inside the cam cover to recirculate into the engine? Would explain the oil seperator, assuming the seperated oil gets dumped down to the sump, while the vapour goes to the inlet manifold. A duff regulator would maybe open up the inlet vacuum to the oil ventilation area.
 

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The engine breather system on a BMW is attached to the inlet manifold, ALL air should travel past the MAF, as it's this that measures how much air is going into the engine, any breather pipes e.t.c that are split allow excess air in and cause a lean mixture, the O2 sensor then picks up excess air in the exhaust and adds more fuel which generally makes the engine run crap.
 

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Discussion Starter · #8 ·
Well I don't want to speak too soon as I know how these idle issues can come and go, but it's as if the idle fairy came in the night.

I started by checking over everything this morning. There doesn't seem to be any oil leaking out the cam cover gasket, or at least not the gushing kind you'd expect if the gasket was folded up under a corner or something. A little residue maybe, but probably from past leaks around that rear area of the cam cover. I pulled that pipe off again (that goes down to the oil seperator/air regulator), and pushed it back in. I also noticed that the idle revs rise when pulling that pipe off, and also when opening the oil filler cap. I put a latex glove over the oil filler cap and it was being sucked in, which would suggest a resonable vacuum being held in the cam cover. So I really couldn't find any serious problems.

So I take it out for a run and it didn't show the slightest problem, idling or through the revs. It nicely drops to above 1000rpm, pauses, then slowly drops to about 700rpm, as it should. I couldn't repeat the symptoms of last night at all.

I can still smell the burning through the heater (only when stationary), but it could need to burn off all past residue where the oil has leaked before. So I will see how that goes. I'm also keeping an eye on my water level, as someone told me burning antifreeze can also smell like that. Here's hoping there's not some kind of water leak out the rear of the head gasket :frown

So a tentative thanks for your help on this one.
 
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