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  #1  
Old 05-11-2014, 02:36 PM
JuhaV JuhaV is offline
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Default Rough idle and no error codes

After the last track day for this season the car seems to have developed the infamous rough idle symptom when hot.

The symptoms are as follows :

- cold start ok and idling nicely for the few first minutes (elevated idle starting from 1100 and lowering gradually towards 800 rpm)
- after a few minutes and when engine has reached certain temperature, idle become erratic and rpm pump up and down 50 rpm from 800 rpm level
- no mechanical or other strange sounds present, only rough idle
- if pushing gas pedal and lifting rpm above 900 rpm everything smooths out
- engine pulls normally above idle

I have checked the following :

- no error codes present
- INPA shows that idle becomes rough immediately when engine goes into closed loop and lambda values start to hunt the optimal fuel/air ratio
- if activating idle control valve from INPA, idle raises to 1100 rpm and smooths out
- both banks 1 (cyls 1-3) and 2 (cyls 4-6) show symmetric values so whatever is causing this affects most likely all cylinders equally
- pluggin MAF on/off affects the idle but will not remove the roughness
- I removed the brake booster vacuum tube and plugged the hole into the manifold -> no change
- during normal driving and above idle all values including lambda readings seem to be normal
- no obvious visual indication of any air leaks etc.

I am going to change my VANOS unit for a fully factory serviced unit during the winter. However, it would be nice if the engine would work normally before that procedure so that I could see that the VANOS swap itself went well.

What is your feeling, can such rough idle actually be caused by a gradually failing VANOS ? I would except that there would be problems also above idle if that would be a case ?

Are there any other simple checks to be made before I pull out the manifold and start to change all the potentially leaking vacuum tubes ? Any particular tube to suspect ?

At some point I has seen n error code related to gas tank evaporative valve but it is not present at the moment. As far as I understand this is the valve actuated in certain situations to pull out the vapours from the charcoal canister and into the manifold. Could a stuck evaporative valve cause such symptoms and not to trigger an error code ?

br, Juha
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  #2  
Old 05-11-2014, 06:02 PM
kwoffa kwoffa is offline
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I had a rough idle...could not find it even with a gas test...no leaks...and only after my engineer checked all the pipework physically only to find it was vacuum pipe..with a tiny split in the elbow part,the pipe was one of the smallest no bigger than my little finger and split right on the angle...not sure where this is tho.. sorry..but it did sort the rough idle out..
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Old 05-11-2014, 06:26 PM
Grolsch Grolsch is offline
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Sounds like it could be this:

http://www.z3mcoupe.com/forum/showth...ght=rough+idle
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Old 05-11-2014, 08:31 PM
JuhaV JuhaV is offline
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Quote:
Originally Posted by Grolsch View Post
Thanks !

The symptoms fit perfectly with that. I will most certainly check this tomorrow evening before doing anything else.

br, Juha
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Old 06-11-2014, 12:27 PM
Aceman Aceman is offline
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I have had this exact same problem and turned out to be the little rubber cap as in the link above.
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  #6  
Old 06-11-2014, 01:44 PM
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damien damien is offline
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Default Rough idle

Hi mate,if it's only happening when the engines hot I'd say it's the exhaust solenoid in the Vanos,you can get it resoldered,should cure the problem,I had the same problem,my Vanos was growling so I had Mr Vanos replace it,perfect now 👍
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Old 06-11-2014, 05:50 PM
JuhaV
This message has been deleted by JuhaV. Reason: Duplicate
  #7  
Old 06-11-2014, 05:53 PM
JuhaV JuhaV is offline
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It seems that I do not have that small rubber cap in my tank ventilation circuitry at all.

Instead, I have this kind of a setup : http://v2tre.wordpress.com/2014/11/0...ilation-valve/

You can see in the middle fig a manual valve in the end of that hose protected with textile like anti-scuff sleeve. It is something called "Disturbance Air Valve".

This thread revealed that it is only found in german and swedish cars and used for emission tests : http://www.bimmerforums.com/forum/sh...-is-this/page2

It can be seen also here : http://bmwfans.info/parts-catalog/Z3...urb_air_valve/

This makes sense as my car was originally sold in Sweden.

I need to pull out the manifold to be able to check all the tubes.
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Old 06-11-2014, 05:58 PM
JuhaV JuhaV is offline
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Quote:
Originally Posted by damien View Post
Hi mate,if it's only happening when the engines hot I'd say it's the exhaust solenoid in the Vanos,you can get it resoldered,should cure the problem,I had the same problem,my Vanos was growling so I had Mr Vanos replace it,perfect now 👍
Ok, thanks. I will anyway change the VANOS during the winter so it will be taken care. The engine idles rough only when hot. The power delivery is on the other hand ok.

Did you see any power loss due to the VANOS issue or was it only indicated as bad idle when hot ?
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Old 09-11-2014, 03:26 PM
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Gazza Gazza is offline
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Rubber cap as mentioned http://www.z3mcoupe.com/forum/showth...ght=rough+idle

Would the S54 have this same cap?

Mine was idling ok, (not used for about 8 weeks) and then I heard the idle change. Then it wouldn't rev easily and sounds like it's running on four cylinders. I checked the inpa and two faults are showing. Oil temp sensor not working (I knew about this ) and exhaust temp sensor not working. No eml light shows on the dash.

Any suggestions ?
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Old 09-11-2014, 03:38 PM
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Dave P Dave P is offline
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Quote:
Originally Posted by garythefish View Post
Rubber cap as mentioned http://www.z3mcoupe.com/forum/showth...ght=rough+idle

Would the S54 have this same cap?

Mine was idling ok, (not used for about 8 weeks) and then I heard the idle change. Then it wouldn't rev easily and sounds like it's running on four cylinders. I checked the inpa and two faults are showing. Oil temp sensor not working (I knew about this ) and exhaust temp sensor not working. No eml light shows on the dash.

Any suggestions ?
Not listed as fitted to the S54

http://www.realoem.com/bmw/partxref....ur=1&series=Z3
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