Rough idle at start up

[redlinealley]

S52 runs a little rough when I start it up. But runs smooth when she warms up. Anyone have an idea of what part is going bad?

[bluptgm3]

Plugs and spark plug/coil extenders, how old are they? Pre-catalytic convert O2 sensors are a 100k service item.
Any stored codes?

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[Terry F.]

No codes? Do you service it at all? Anything due, filters, etc?

[redlinealley]

No codes and all tuneup parts have less then 4K. Vanos rebuilt with less then 1K

[Terry F.]

Air pump crap all good?

How long until it clears up? Seconds? Minutes?

[redlinealley]

As far as I know it's all good. I just found this old thread. So I'll clean the ICV with carb cleaner and see how it goes.


Screenshot_20170819-221359.jpg

[Terry F.]

Is that your next step?

[rf900rkw]

Terry is on the right track. If the roughness is for less than a minute, you have a small vacuum leak. When the SAI system runs, it jacks the mixture as rich as it dares. When you add positive fuel trims from a leak, it gets arich lopey-hunt until the pump shuts off.

[Terry F.]

You are in better hands now.

[redlinealley]

The roughness is for a couple of minutes until the car is warmed up. If the air pump system would be leaking is that part of the evap system? Also would I throw a code then, because I don't have any codes.

[rf900rkw]

If it goes on for more than 30 seconds or so, then look to the ignition system. Also check the fuel trims with an OBDii scanner. Just because there isn't a code doesn't mean they are fine. For example, a P1188/89 code sets at 10.3%. You could be 10.0%... same running problem, but no code.

[redlinealley]

Ok thanks, I'll have to have my buddy use his scanner

[Bilito]

Hey Red, Did you ever clean that ICV?? If so how did it run after that??? and how hard was it to get at that valve.
I am asking because I have the same issue

[rf900rkw]

On these engines (the M54 is a totally different animal), the IAC valve can not cause rough running. If it sticks, the idle speed will be wrong. And if it sticks, you need to figure out why. The usual cause is those crap aftermarket air filters.


While we're on the subject of fake internet lore. O2 sensors do not just wear out. They are murdered. The ceramic heater can be broken by shock. The sensor itself can be contaminated. But they don't just die at xxxK miles. The most common cause of failure is the same as what kills cats; contamination from engine oil, antifreeze or unauthorized fuel additives. I don't know who started the 100K mile thing, likely someone selling O2 sensors. It's not true.

[redlinealley]

I just finished up cleaning the ICV and NOW I have high idle, which I didn't before. The ICV didn't rattle inside before cleaning and now after cleaning the part inside moves back and forth quite nicely. Also seems to run smoother. Wish I would have know to clean it when I had everything torn apart a couple of months ago. But it only took 1hr.