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Old 02-23-2010, 06:41 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
How do diagnose a sudden and disturbingly unsettling cold-engine misfire (vanos?)

Advice sought for debugging a suddenly severe & disturbingly intermittent cold-engine misfire.
EDIT DESCRIPTION: Random cold-start single-cylinder misfire with concomitant fuel shutoff lasting only a single ignition cycle (or OBDII code clear in lieu of an ignition cycle).

My story:
Two nights ago my 2002 525i stumbled a bit upon cold-engine start (about 55F ambient); but within a minute or so it ran fine as always.

Last night, at about 45F ambient, the entire BMW bucked like a washing machine after I started it up and barely was able to crawl out of the garage. I had to actually FLOOR the gas pedal to get the E39 to creep up a simple hill, amazingly, it was stumbling so badly, as if it were on a single cylinder instead of six.

As if to chastise me for neglecting some critical maintenance procedure, the Service Engine Soon (SES) light blared yellow at me. It was horrid as I was defenseless and uncertain what to do next but I was meeting someone so I had to drive.

This unsettling stumbling remained for about 15 miles, even though I was able to attain freeway speeds ... until I shut down the car. Miraculously, as if to toy with me, when I started it back up 2 hours later, there was no stumbling. I did some errands at various stores and again, even with three or so additional starts, no stumbling. (The SES is still lit brightly and ominously though, as if to say ... "I'm still here" ... whatever it is indicating.)

Of course, I need to check the OBDII codes (I have been borrowing an OBDII tester but maybe it's time to finally buy my own).

Contrary to what I've read on Bimmerfest, I visited the fabled Autozone but, the counterman said in California it's illegal for AutoZone to test your car. I next tried Kragen and they don't test either. AutoZone pointed me to AAMCO but I didn't know where they were. Plus, I don't mind getting a good OBDII tester - the only thing stopping me is that I want only one and there are so many out there I'm not sure which one to get.)

In the meantime, to start my debugging sequence, I looked up the double VANOS symptoms, but they seem to be "gradual" misfire upon cold start - which happens slowly, over time. This misfire is sudden and unmistakable - almost as if something broke or fell off catastrophically!

Last edited by bluebee; 03-08-2010 at 10:10 AM.
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