I have a 2000 328i automatic (M52TUB28). Weather is pretty cold and rainy here now.
When the engine is cold (needle has not reached the first line on the temp gauge yet) and I let it idle, the revs dip to around 500rpm sometimes, but you hear it corrects itself pretty quickly by overshooting the revs a bit and then coming back to a normal ~700rpm idle. That happens every few seconds, until the temp gauge reaches the first line, then everything is fine. Engine revs and runs perfectly otherwise.
Since this morning, it also stalled a few times when the revs dip, which became pretty annoying quickly.
Now, this is the 3rd BMW I've had with these symptoms and in the last two (E36 318i (M43B18), E46 318i (N42B20)) I never managed to properly fix this (replaced vacuum hoses, ICV, etc), so it's pretty annoying
DME gives no error codes. Car gives some white smoke after a cold start, but goes away after driving it for a bit. Supposedly the last owner replaced the CCV recently so not thinking in that direction right now. Any ideas?
It sounds like you have vacuum leaks. The intake manifold needs to be smoke tested. At this age all of the rubber engine hoses need to be replaced.
Those symptoms sound like bad vanos seals.
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The dipping idle on the old six would only do it when on cold start up, could definitely be the vanos
Thanks, will check the intake boots and other vacuum hoses soon for leaks.
Any way to test the VANOS seals? Anything I can check with INPA?
Today it was cold but not raining and it idled much better, if that provides any clue..
The only way to find all of the vacuum leaks is to smoke test the intake. Bad VANOS seals typically show up as an acceleration flat spot between 2000rpm and 3000rpm. At that age they need to be replaced. Go to http://www.beisansystems.com/. This company sells the best replacements and their procedure is easy to follow.
The link posted above (besian) lists symptoms of failed vanos seals. Idle dip/stall is one. For some reason this only happens to m52tu cars. M54 uses same vanos but never have the idle dip/stall. Smoke test is a good idea too but the stalling is the vanos seals if it happens only when the temp gauge is just coming out of the blue. Replace the seals.
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