unfixable misfire

[mx0321]

i have a 2003 Z4 3.0i with 67k miles on it. it has been misfiring since the beginning of january.

this happens randomly about 2 - 3 times a week and seems to happen with the ac off (ac has to be off) and when the engine is at operating temp (most of the time). when i start my car, within seconds it'll start misfiring for about 5 - 8 seconds, the rpm needle will bounce at 500rpms, then it'll stop misfiring and run normal. i can kind of feel when its going to happen because the engine feels like it runs little rough.

i've brought it to the dealer sh!t ever since it has started. they recently had the car for a month and couldn't replicate the problem (so they said). the service manager also threw me under the bus by telling me i should maybe go to another shop (i have CPO warranty, its f'd up). so far they have done a few things.

-ran a cleaner through the engine 3x
-reprogram the computer
-replace the spark plugs
-replace the ignition coils
-replace the fuel injectors

next monday i'm going to a shop and going to have them do an inspection on my car and get ideas from them. Any ideas guys?

[nickpapa]

maybe its the gas your using? if there were misfires it should throw some codes. any idea if the dealer told you what codes popped up?

since it is intermittent my first guess would be the gas youre using. id switch stations (if you go to the same one) and see if it helps. and use a higher octane gas if you don't put super in it already.

if it only happens at operating temp, it could also be the oxygen sensor/sensors. bad oxygen sensor/sensors only act up when at normal operating temperatures, not when the engine is cold.

[mx0321]

we have 91 octane so that's what i usually use. i have tried different stations i get the same results. i've even used 93 octane when i go out of state and it still does the same thing. The dealership did check for quality of gas and amount of alcohol in it and said it was fine. less than 5% alcohol. oxygen sensors... i've thought about it, is that something i can do myself?

[nickpapa]

you can do it yourself but if you have warranty I would maybe ask the dealer to run a test on them to see if they are bad. this way if one of them is bad (i believe there are 4) it will be replaced under warranty.

[tofu4]

Clean out your idle air control valve its next to the the throttle body. Over time the unit gets sticky from sludge and grime. When this happens it cause misfires and horrible idle.

[Chuck I]

Originally Posted by mx0321

next monday i'm going to a shop and going to have them do an inspection on my car and get ideas from them. Any ideas guys?

Your shop should be able to run the diagnostics and pull the faults. That will tell them exactly which cylinders are misfiring and how many times the event has taken place. That could narrow it down to a cylinder or if it's random it would point back to one of the common parts. Hope you figure it out... Chuck I

[mx0321]

After going back and forth with BMW after my CPO ended, it ended up being the flywheel. They said it had excessive play in it which was causing the knock sensor to misinterpret the knocking. Don't know if that makes sense, but it hasn't misfired since (a month now).

[inTgr8r]

Very interesting... glad they finally found it for you.
Thanks for the update!