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Old 08-23-2014, 12:04 PM
Join Date: May 2008
Location: Canada
Posts: 847
autoque is on a distinguished road
Exclamation Advice needed on rough start/idling

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? Yeah, I'm throwing parts at it but I think I'm this close to finding out the root of this problem. BTW, no codes.
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Old 08-24-2014, 07:40 AM
Join Date: May 2008
Location: Canada
Posts: 847
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Oh, BTW, the eccentric shaft sensor has already been replaced but no difference.
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Old 08-24-2014, 10:47 AM
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Location: Los Angeles
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That is not the proper way to diagnose or fix a modern car.A simple scan with DIS or ISTA will tell you the problem with a very high probability to be fixed at first attempt.
Here is how the valvetronic works:the TB is closed at start-up and opens completely a few seconds after the engine is running.The function of the TB (regulating engine RPM and output) is performed by the Valvetronic:min valve lift=idle,max valve lift=max power,and everything in between.If there is a malfunction in the Valvetronic system registered by the ECU,valve lift is set to max and the Valvetronic is disabled.At this point the engine is controlled exactly as a conventional engine-with the TB.
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Old 08-24-2014, 06:25 PM
ard ard is offline
Join Date: Mar 2006
Location: Sierra Foothills, California
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from elsewhere:

Originally Posted by ard;
every BMW motor with VANOS valve control will eventually suffer from 'vanos solenoid issues'....some more than others.

the basic issue is that the solenoids- which are bathed in high pressure oil- become fouled over time, causing sluggish operation. In addition the o-ring seals around them become hard and can leak, allowing opil to bypass.

As a result the operation becomes sluggish.

Eventually they will trip a code..eventually.

In the S62 world we have learned that cleaning the solenoids and replacing seals is a maintenance item.

There is a functional VANOS test- available on the GT1, Autogenuity, etc systems- that will actuate the vanos and report how quickly and completely they move. It is usually obvious when one isnt operating properly. Indeed it is common for 8 YO cars to not throw a code but to still fail this vanos test.

Not sure about these motors, but thought this might be useful...

agree that scanning the DME with something way more involved than a OBD code reader is the way to go...
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