Very lumpy idle

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Tilly
Joined: Wed 26 May, 2004 20:45
Posts: 428

  M roadster S50
Location: Sussex

Very lumpy idle

Post by Tilly » Sun 04 Apr, 2010 16:37

Very lumpy idle and failed the MOT emissions test. Car is fine when above idle speed. Vanos replaced last year(Dr Vanos) and car ran perfectly for a number of months then the lumpy idle started and gradually got worse when engine hot. No starting problems from cold.
Garage bemused and cannot suggest a solution. No faults showing on the diagnostics. However cam is showing a 17 degree retard. They managed to adjust the cam to get it through the test but the idle problem continues and cam retard is still occuring. The mechanics are not happy they had a solution and over the last month have tried a number of things.
Cam sensors replaced. MAF checked and no air leaks in the system. Their only suggestion and also that of Chris Gant at Dr Vanos is a Vanos solenoid may be causing a problem in retarding the cam without showing a fault.
Anybody got any other suggestions I can relay on to the mechanics.

bugsy
Joined: Wed 01 Apr, 2009 10:12
Posts: 47

  M roadster S50
Location: Sutton

Post by bugsy » Mon 05 Apr, 2010 18:45

Have you tried the ICV?

These are from other posts having searched for Engine Idle:

two days before M O T , typical, engine developed really bad idle also cutting out.suspected air getting in after airflow sensor after reading other posts,seemed probable as engine revs also slow to come down after revs.turnd out to be cranckcase breather pipe come adrift. lucky me , nice easy fix .pipe halfway along block under inlet manifold , awkward to get to but just a matter of reconnecting and tightening jubilee clip, engine now right as ninepence{that means okay}

http://www.zroadster.net/forum/viewtopi ... hlight=icv

Firstly you need to carry out a Vanos check using the Diagnostic machine, they just plug the Computer into the Diagnostic Port and run the test from the tests menu. It operates the solenoids and advances and retards both exhaust and inlet sides while the engine is ticking over. The readouts tell you if there is a fault but not what type of fault. It could be the inferior seals and O-rings which cause no noise but fail over time. It is usually the excessive play in the bearings which make the Vanos growl so you can have one without the other. With my car it was the ‘O’ rings which failed on the exhaust side. The main part of the Vanos is robust and the actual solenoids only occasionally fail.

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Jonttt
Z Register member
Joined: Sun 28 Dec, 2008 16:32
Posts: 6536

  M roadster S54
Location: Liverpool

Post by Jonttt » Mon 05 Apr, 2010 19:27

Saw this thread on Z3mCoupe re S50 rough idle so might be worth a read ?

http://www.z3mcoupe.com/forum/showthrea ... #post84667
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Tilly
Joined: Wed 26 May, 2004 20:45
Posts: 428

  M roadster S50
Location: Sussex

Post by Tilly » Mon 05 Apr, 2010 20:48

Thanks Bugsy for the suggestions.

The ICV was one of the first things that came to mind and a new one fitted. Had absolutely no effect. The crank case breather pipe should have been checked but you never know. However, would tend to think that would cause more problems than just a lumpy idle. As to the Vanos, been there, done that and got the tea-shirt. The Vanos readout shows no fault whereas when the seals failed last year a fault code came up.

Jonttt thanks for the link.

A missing small runner T-Piece could easily be overlooked. As above I’ll get that looked at tomorrow.
It’s the cam retard that’s really baffling me. Take out the Vanos, MAF and Lambda sensors, not a lot left. Either way when we finally get it sorted I’ll post on the site to help those with similar problems in the future.

Thanks both of you for your help.

aj2007
Joined: Wed 01 Aug, 2007 19:22
Posts: 435

  M roadster S50
Location: Newcastle-under-Lyme, Staffs

Post by aj2007 » Mon 05 Apr, 2010 20:50

Tilly

you got PM

Ade
Image

Tilly
Joined: Wed 26 May, 2004 20:45
Posts: 428

  M roadster S50
Location: Sussex

Post by Tilly » Mon 05 Apr, 2010 21:03

Thanks Ade.

If I cannot get satisfaction, I know I am tempting fate with that comment, I'll do what you suggest.

Tilly
Joined: Wed 26 May, 2004 20:45
Posts: 428

  M roadster S50
Location: Sussex

Post by Tilly » Fri 09 Apr, 2010 20:09

Problem solved.

The inner o-ring on the exhaust solenoid of the Vanos had split. Although the unit was recently replaced, Chris Gant from Dr Vanos was of the opinion was that one of the seals may have been damaged during the refitting of the Vanos. The seal was indeed damaged and fitting a new seal curred the problem.

Once again thanks to the members who provided some valuable help.

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