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Idle surge

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worzel View Drop Down
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Joined: 17 Nov 2017
Location: Merseyside
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    Posted: 20 Nov 2017 at 10:08am
Hi

Any ideas on this one- have had plenty of suggestions (all printable) so far but haven't resolved the problem.

An odd one- I bought a very nice low mileage Feb 1991 525i 4 years ago.  Low mileage and clearly very well looked after with both a faultless body and as new interior.  Not had any significant problems with it except for one which, I confess, has beaten me.

In every respect the engine runs faultlessly except when coming to a dead stop.  At a stop the engine surges for about a second or two and then idles faultlessly until the next stop.  This usually (but not always) occurs once fully warm- during warm up it usually behaves itself.

What I've done so far- 

I removed the inlet manifold, replaced the seals/gaskets removed the hose for the fuel pressure regulation and the one that feeds the idle valve, siliconed new hoses into place and relocated the idle valve to a more convenient spot at the same time fitting new silicon air intake hoses.

I've also replaced with new Bosch items the following- idle valve, maf, tps, air intake temp sender, air filter and new intake elbow from maf to throttle body.

I've also altered the intake system slightly- the engine now only gets air coming thru the maf- the breather is now vented to atmosphere.  My reasoning on this is that the breather is feeding air into the intake after the maf so this isn't actually being metered so might be affecting the settings.

I know the symptoms described would suggest some sort of air leak on the induction side but if so I can't imagine where it might be.

Any ideas on this one- all suggestions gratefully received.

Regards and thanks


John
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