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
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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