E36 M52 intermittent uneven Idle

[bababa]

Hi guys,

I had an interesting experience with my 328i last night. No problems with it for months, runs as smooth as a nut until I stopped at the shops on the way home from work. I was out of the car for about 25 minutes and when I got back to the car and started it, the idle seemed quite lumpy.

It drove home absolutely fine, but at every junction or set of lights on the way home the idle would be pretty rough. When I got home and popped the bonnet, the misfires seemed evident by the fact that the engine block was occasionally visibly jerking from left to right - the check engine light wasn't illuminated either.

Went indoors to get the code reader, and it revealed a stored code (11 D4 - VANOS Mechanically Stuck), but I've had this code a few times before with no change to the performance of the car.

However, I went and restarted the car about two hours later and it was sweet as a nut again - as it also was this morning.

Could this be the "popular" cam position sensor failure beginning to manifest itself?

I can't find any visible air leaks - I replaced the intake boot from the airbox to the throttle body about three months ago when I noticed a few splits in it....

Thanks for any advice!

[8Tech]

If you have a recurring fault code, why are you dismissing it all the time? If you keep getting the same code, then that fault needs dealing with before you look elsewhere!

8Tech.

[bababa]

8Tech said:

If you have a recurring fault code, why are you dismissing it all the time?

Good point

TheEnd had previously indicated (http://www.pistonheads.com/gassing/topic.asp?t=1068207) that it's quite a common fault and doesn't necessarily indicate that the VANOS actually is stuck. Whilst I do hate having stored fault codes and it was on my list of things to investigate, as there were no obvious running problems with the car and the VANOS seemed to be working fine it wasn't really at the top of that list!

ETA: But actually, you're probably spot on, thinking about it. I guess rough idle but no problem with driveability (other than a moderate loss of midrange torque which I probably wouldn't have noticed on the local roads back from the shops) is exactly the symptoms one would expect if the VANOS were mechanically stuck. I guess it freed off in the couple of hours the car was stood and has been fine since with no further codes stored.

Fault code in "potentially indicating actual problem" shocker - who'd've thought!

Wonder where I go from here then - overhaul/reconditioned VANOS, I guess.

Edited by bababa on Thursday 19th April 18:28