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Old 11-10-2012, 04:42 PM
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DSXMachina DSXMachina is offline
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Location: New Hampshire
 
Join Date: Dec 2007
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Mein Auto: 335i E92 TiAg 6MT ED
Quote:
Originally Posted by autoque View Post
Not quite sure, even after more than three years of trips to various dealers and master techs, no one knows what's wrong.

I've got a warm start rough idle which lasts one to two minutes after the ignition. This started right after replacing the cylinder head under warranty for a tapping noise, a well known issue in the N52 engine. They changed the spark plugs, coils, MAF and cleaned various parts, tuned up the timing of the valves, disassembled and reassembled, the symptom got a little better, but never disappeared. So my final desperate move, throw expensive parts at it, especially suspicious is the cylinder head unit, which started this long painful journey. I'm out of warranty so I'm picking up the tab, but the dealer's willing to forgo the labor cost since they know I've been having this problem early on. However the dealer doesn't know whether the replacement will lead to fixing the problem as their diagnostic device tells nothing's wrong.

The whole head costs like over $5000 so I thought replacing the valvetronic and vanos is more sensible to a rough idle problem. By the way, absolutely no fault code stored except a code was found about a month ago indicating an error with the vanos solenoid valve, so the dealer replaced it rather than cleaning it and using it again, hoping it would solve the problem. But no go.
The valve train was assembled incorrectly, or a defective component was installed. I'm going for the defective component. Why? Because it's a warm start issue that fades in a few minutes, and manifests itself at idle.

You are getting gaffed big time. BIG TIME and you don't even realize it. You had work done on the warranty. After the work was done you had an issue. They have fiddled and diddled for months and now they say they are willing to do the labor for "free" if you buy the parts. But they don't know if that's going to fix the problem. (Therefore, thanks for the 5000 bucks, but oh well.)
You need to say good-bye to that dealership, find a good indy who knows the N52, and get the thing fixed right. I have a very good idea exactly what's wrong. It isn't the valve train per se, but it does neither of us any good for me to 'guess' in this instance. Suffice to say, if you have the valve train replaced you will probably leave with the same problem.
A good indy will hook up a Verus scanner, or equivalent, and graph every variable he can, then save the graphs. There are roughly 40 parameters which can be graphed. By comparing what happens and when, especially just as the idle smooths out, he will see what I suspect. I don't know if you have SAE certified techs in Canada, I believe you do. Look for someone who has what's called L1 certification. He'll figure it out.
Expect the cost to be less than $5000.
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