Unstable idle.

What do you guys think would be most probable reason for unstable idle?
Happens only once in a while and doesn't seem to cause anything else (yet?).

Idle can be wondering between 1000 and 500rpm. It happens only once in a while, but i feel like it's coming more often nowadays.
According manual 850rpm is normal for this engine.

It has been -10C (14F) or colder for long while, but i do visit underground shopping mall parking quite regularly for melting some ice and snow off.

Originally Posted by lgr122

What do you guys think would be most probable reason for unstable idle?
Happens only once in a while and doesn't seem to cause anything else (yet?).

Idle can be wondering between 1000 and 500rpm. It happens only once in a while, but i feel like it's coming more often nowadays.
According manual 850rpm is normal for this engine.

It has been -10C (14F) or colder for long while, but i do visit underground shopping mall parking quite regularly for melting some ice and snow off.

maybe check your idle control valve and see if its clogged up and needs cleaning, but i might be wrong.

Originally Posted by sjbmw328i

maybe check your idle control valve and see if its clogged up and needs cleaning, but i might be wrong.

I think that might be some possible cause according search on earlier threads, but still wondering if there can be also some other good ideas.

Check the DISA. Relatively easy to inspect. Make sure there is at least light resistance to the plastic flap while turning.

I had a rough erratic idle (between 700 - 1100 rpm) at about 110-115k miles on the clock. DISA was completely broken. Replaced (purchased at local dealer for $250) & it fixed the issue. Not sure if you mentioned you had any codes - but mine threw p0174 and 171(? Not completely sure) Both indicated air issues.

Originally Posted by whinojosa

Check the DISA. Relatively easy to inspect. Make sure there is at least light resistance to the plastic flap while turning.

Since you brought up that, here is a old DIY video from way back of how to to take out/clean/ and install the Idle control Valve. http://www.bimmerfest.com/forums/sho...d.php?t=496398 During the video, it also shows what the DISA looks like and how to take it out. Maybe check with those first, and if problem still occurs. Hopefully another fester will be willing to help on this thread.

Hmm... i'll check those...
still about couple weeks before it's time to oil change, probably going to be ok till then.

Fixing a vacuum leak (or two, or three) and replacing the VANOS seals seemed to solve this problem once and for all on my car. I've had recurring vacuum leaks since without such a bad fluctuation in the idle speed, so I think the VANOS might have been the key.

I wouldn't be surprised if some hose is bit fractured also, freezing weathers can be bit nasty on those. Anyway, it's not like some problem quite yet, but i'm trying to see symptoms before it become problem.

I am not familiar with those engines in the cars like yours, however bad VANOS seals cause poor idle in the M52tu motors we run in over here. Might be your issue.