[tgeho_e92]

Hi I've seen a couple of posts about this but it seems that my car does something different than everyone else's. Most times when I start my car on a cold start it starts and goes to 1,000RPM for a second before the computer figures everything out and it goes to 500-700RPM. As soon as it equals out it oscillates (best word I can come up with) between 600-800RPM until it chills out and smoothens.

Could this be something serious or is it the computer just fluctuating the RPM to find the "just right" spot.

[e90yyc]

Subbed for results. I have this exact problem sometimes. Doesn’t seem to fit the description others with “jumpy” idles.

[nsjames]

the computer does not hunt for RPM speed unless it's having problems controlling it.

mine idles up for the cold start, then idles down and stays rock steady.

check and clean the vanos solenoids and screens, check for vacuum leaks and un metered air, check valvetronic things.

edit:
and if you've got a disa manifold, check the disa motors.

[e90yyc]

Originally Posted by nsjames

the computer does not hunt for RPM speed unless it's having problems controlling it.

mine idles up for the cold start, then idles down and stays rock steady.

check and clean the vanos solenoids and screens, check for vacuum leaks and un metered air, check valvetronic things.

edit:
and if you've got a disa manifold, check the disa motors.

Noob question but what is the best way to check for vacuum leaks?

[nsjames]

Originally Posted by e90yyc

Noob question but what is the best way to check for vacuum leaks?

smoke machine.

but the hackjob garage method is to spray something combustible where you suspect there might be a leak and listen for the idle speed to change.

I built a paint can smoke machine because I got tired of wasting time with other methods.

[e90yyc]

Originally Posted by nsjames

smoke machine.

but the hackjob garage method is to spray something combustible where you suspect there might be a leak and listen for the idle speed to change.

I built a paint can smoke machine because I got tired of wasting time with other methods.

Gotcha. So just form airtight seal between smoke machine nozzle and TB or intake.

I have a smoke tester (ghetto paint can one too) sitting in my garage but I haven’t gotten around to this yet. I feel like the smoke it puts out isn’t thick enough to be easily detectable, but maybe I’m wrong.

[nsjames]

basically.
just make sure it's regulated to 1-2PSI so it doesn't blow everything apart and hook it up.

if yours isn't making enough smoke, decrease the ohms on the element and it gets hotter.
Mine takes 6-7amps of current IIRC.

[tgeho_e92]

Originally Posted by nsjames

the computer does not hunt for RPM speed unless it's having problems controlling it.

mine idles up for the cold start, then idles down and stays rock steady.

check and clean the vanos solenoids and screens, check for vacuum leaks and un metered air, check valvetronic things.

edit:
and if you've got a disa manifold, check the disa motors.

Wouldn't those things cause other issues other than a jumpy idle. My car runs like butter other than SOMETIMES a jumpy idle. I'm a noob to the noobs with BMW so my questions might be obvious but I'm blind as heck.

[nsjames]

a small intake leak is proportionally a much larger leak at idle than at WOT.

likewise you need the valvetronic to be it's most accurate at idle, because you're dealing with tenth of a mm things.

[tgeho_e92]

Okay so I wanted to give an update. I unclipped the vanos and wiped them down really well. I haven't had the issue since. Having said that, I live in Allentown PA which is getting warm right now. Above 55 at night. I have no idea what was happening but it's not happening anymore. I'll give another update when I get my VCG replaced. I know that will probably not have an effect on idle but I can have the tech that's doing it check other things like vacuum leaks etc.

[e90yyc]

Thank you for following up. I'll try cleaning my vanos solenoids again but I did a few years back and not sure it made any difference. That said it's free and takes 10 minutes.

Keep us posted on the outcome of your VCG and anything else you find!

[yonversace]

Originally Posted by tgeho_e92

Hi I've seen a couple of posts about this but it seems that my car does something different than everyone else's. Most times when I start my car on a cold start it starts and goes to 1,000RPM for a second before the computer figures everything out and it goes to 500-700RPM. As soon as it equals out it oscillates (best word I can come up with) between 600-800RPM until it chills out and smoothens.

Could this be something serious or is it the computer just fluctuating the RPM to find the "just right" spot.

I think it’s normal (only on start up) mines used to do it terribly until i replaced the MAF

[ctuna]

Coils and Plugs
A coil starting to go bad can cause a jumpy idle
it may not throw a code yet but it is on the way
to failure . Especially accompanied by gas milage loss
and power loss.
There are other things that will cause it to but if your car
is past 70k on a N52 or N51 it is something to take
look at.
I just went through this .
It was jumpy then cylinder 6 finaly failed .
I had changed plugs about a year ago.

[tgeho_e92]

Originally Posted by ctuna

Coils and Plugs
A coil starting to go bad can cause a jumpy idle
it may not throw a code yet but it is on the way
to failure . Especially accompanied by gas milage loss
and power loss.
There are other things that will cause it to but if your car
is past 70k on a N52 or N51 it is something to take
look at.
I just went through this .
It was jumpy then cylinder 6 finaly failed .
I had changed plugs about a year ago.

92k miles and no car fax records of them being done what's a new set of plugs cost?

Edit: I just checked my mileage. I get 25 mpg average. Extra-Urban conditions.

[Schmitz]

I have this problem, but only on warm starts. Hoping replacing my valve cover gasket will fix it...

[Soden82]

Good to see you fixed the issue. A vacuum leak would cause those symptoms you were having and could be worth just replacing them for peace of mind since it takes about 20-30 minutes to do and costs less than $20.

[tgeho_e92]

*UPDATE* I got my valve cover gasket replaced by a local Indy shop known for BMWs. As it turns out, I had a massive leak that most definitely caused the uneven idle. I had it done 4 days ago and the problem no longer persists. Actually I feel like the acceleration from stop is SIGNIFICANTLY smoother. I initially thought that was cause by my transmission. Funny enough that even seems smoother…. Probably in my head but all around a significant increase in stability and performance.