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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Rough warm start, but fine without eccentric shaft sensor



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      08-23-2014, 10:55 AM   #1
autoque
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Exclamation Rough warm start, but fine without eccentric shaft sensor

I've got a '08 N52 3.0 naturally aspirated motor. At every warm start, the engine runs rough for like 1 to 2 minutes. It almost disappears after about 2 minutes but a sensitive person can still feel some unevenness in idle whenever I'm stopped.
But when I unplug the eccentric shaft sensor, the symptom doesn't show up anymore. From what I've researched, unplugging the eccentric shaft sensor disables valvetronic and the valve lift is set to maximum at idle.
I've also heard, for N52 engines, the valve lift can't be adjusted as it's automatic.
So which parts of valvetronic should I replace to fix this issue?
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      08-23-2014, 11:23 AM   #2
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The sensor itself.
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      08-25-2014, 06:41 AM   #3
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I forgot to mention the eccentric shaft sensor was replaced, but no difference.
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      08-25-2014, 06:45 AM   #4
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When you unplug it and look in, do you see any oil?
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      08-25-2014, 12:00 PM   #5
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Quote:
Originally Posted by TheSt|G View Post
When you unplug it and look in, do you see any oil?
Yes, the eccentric shaft sensor had oil in it. Cleaned and plugged back in, same symptom. So replaced it but still no difference. It must be something else. BTW, coil and spark plugs have been replaced before, as well as maf but no change. Something in the valvetronic I think... I tried unplugging the vanos solenoid to disable vanos, but the symptom remained, so it may not be vanos, but suspicion is on the valvetronic.
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      08-25-2014, 02:03 PM   #6
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Quote:
Originally Posted by autoque View Post
Yes, the eccentric shaft sensor had oil in it. Cleaned and plugged back in, same symptom. So replaced it but still no difference. It must be something else. BTW, coil and spark plugs have been replaced before, as well as maf but no change. Something in the valvetronic I think... I tried unplugging the vanos solenoid to disable vanos, but the symptom remained, so it may not be vanos, but suspicion is on the valvetronic.
Have you pulled the codes? That would be the first place to start. The valvetronic is not particularly known for failure.
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      08-25-2014, 03:10 PM   #7
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Absolutely no codes whatsoever. Checked at the dealer too.
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      08-25-2014, 03:29 PM   #8
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Quote:
Originally Posted by TheSt|G View Post
The valvetronic is not particularly known for failure.
I'd think so too, but I can't pinpoint the problem at the moment to any particular part. Took off the valve cover and camshafts/eccentric shaft look fine with no particular wear pattern.
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      08-27-2014, 07:21 PM   #9
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I have the same problem and been trying to solve it for months. No luck so far. The other thing I also noticed is if I do not drive the car for a day or longer then even a cold start takes a little longer, otherwise cold starts are fine.
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