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      03-06-2013, 02:11 PM   #199
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Drives: 2008 335xi 6spd Coupe
Join Date: Dec 2007
Location: Boston

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2008 335xi  [0.00]
Originally Posted by SDSUDons View Post
AWD Addict, any luck? I've had mine in the shop so many times and gotten the same, "we cant find anything wrong" except I KNOW something is wrong. Started right when I changed the plugs. I used to wrench on cars myself at a hot rod shop, and between that and driving the car every day, I know when something is wrong. I read the whole forum and noticed that it seems everyone has tried something that would logically make sense, but to no avail. Something to add, I noticed a slight lack of power while driving, at all speeds. Also, the gas mileage seems to have taken a noticeable hit. I was averaging around 450 miles per tank, and now I am getting about 300 since the spark plug change/random rough idle. You notice that? LOVE the fact that it doesnt throw codes either.

Side note, I have been recording data for the rough idle and comparing it to the normal idle. I am going to have a few trusted mechanics around town look at it as well and see if they can wrap their heads around it. Let me know if you have any updates. Thanks!
Been working on it with my independent mechanic now that I'm out of warranty. THe answer is no. I can tell you it's a miniature misfire though, as it's worse when my plugs are bad.

I'm inclined to believe its just something that's a part of the car at this point, coincident with the other finicky elements like injectors, coil packs and plugs. I think this car is just a very fine tuned vehicle with very little margin for error given the amount of technology used for its operation.

I think we should all be changing plugs every 20k miles (minimum, if you're tuned, less). I'm at almost 20k since mine were done, and I've noticed my mileage is down too. I'm about to get them swapped. I'll record a couple tanks and report back if that's in fact related.