Rough Idle at Start Up, Stop Lights, etc

[VaTechZHP]

I've been having a consistent idling issue for a week or so now which I had originally attributed to a torn lower intake boot. After replacing both lower and upper boots, there was no change in the cars ability to hold a steady idle.

The car seems to let the rpms drop to around 500 and you can feel the car start to stumble and shake if you are sitting at a stoplight.

My mechanic said he noticed the tear in the boot, but also noticed my CCV was on its way out. Is it possible that the CCV is also contributing to this idle problem?

While replacing the lower boot, I pulled the ICV and cleaned it with MAF cleaner. Does the ICV really only assist on cold start ups to adjust idle until the car warms up enough to idle unassisted? Could the ICV be the culprit of this erratic idle?

While the revs seem to dip down to 500 or so, the car will then compensate and rev up to almost 1500, smooth back down to around 7/800, then dip to 500, and repeat this process. The car almost feels like it is going to stall, but then catches itself.

I have not noticed any driving issues once the car gets going except that the pedal seems very twitchy in that if I lift off throttle to coast, the car will buck slightly as if I completely got off throttle after going WOT.

The CEL is on, and I had the codes pulled at Advance and they seemed to point to lean conditions which would make sense if I was sucking in unregistered air into the A/F mix.

Any thoughts would be great before I throw more parts at the car.

TIA!

[HokieZHP]

My car does this too to some effect. It will drop to about 500 then spring up to 1000-1200 then settle again. My CEL is not on though. It happens very rarely so I haven't bothered with it but I'm also interested in what you all think it is.

[aurelius]

What is the fault code number?

[danewilson77]

ICV or vacuum leak. Code will be helpful. Could be a myriad of things.

[VaTechZHP]

I'll have to dig through the car again and see, luckily the CEL is still on (not like its a good thing haha) so I could get the codes pulled again if I can't find them.

[Oli77]

About your question on the ICV and cold start ups only.

I can tell you this, I recently cleaned my ICV because I was having similar issues all though the changes in rmp where not as drastic as yours. Mine would simply dip low when coming to neutral (stop).

On startsup, mine would go high, then low then steady (on rmp) nearly all the time.

On cleaning the ICV, I noticed nearly 90% of starts are now high and then quickly and steady down to middle rmp speed (cleaaaaaannnn).

Cleaning the ICV also significantly reduced the number of instances when idle would dip too low on coming to a complete stop by 80%.

Perhaps a more thorough cleaning would get it perfect.

I have 75K miles and its all original stuff.

[danewilson77]

Even if light goes out...code will be stored.

[VaTechZHP]

Thanks Oli, I just sprayed some maf cleaner in there. I'll pull it back out and clean it with some Brake Clean and see if that helps. It certainly looked dirty in there when I pulled it out.

[3ZHPGUY]

I had a similar problem last month and took it to the experts at Ganley BMW. It turned out to be a DISA valve. This is the rectangular box attached to the intake behind the dip stick. The tech notes stated that it had fallen apart and the parts were sitting in the intake "NOT A GOOD THING". The OEM part was $250.00 and all total my bill was over five with a few other thing included.

In looking on the net after I paid the price, I checked YouTube and the job looks simple as long as you know what your looking for. For more information Google BMW DISA.

[danewilson77]

Yes. Simple.

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