[matthatchett]

In September of last year, I purchased my 2006 BMW 325i. My car has 72k on it and I'm not real sure what all has been serviced, replaced, etc. due to no service records. I have had problems galore out of this thing, everything from an oil leak all the way to having the motor replaced. Anyway, now there is a new issue. A few weeks ago I noticed at a stop light the engine had a rough idle and the service light came on. Checked the service light and it came back with two codes. The first code was Bank #2 Oxygen Sensor (or something along those lines) and the second code was Cylinder #3 misfire. Replaced the O2 sensor and #3 coil. First code never came back but the Cylinder #3 misfire code keeps popping up. Every time the engine is at idle, it is fighting for rpm's; 500,700,800,600. It never settles down and I can't really tell if it continues at higher rpm's.

My next thing is to replace all 6 spark plugs and all coils. That may be a little extensive but I'd rather know neither of those things are the issue. If that doesn't work, I was thinking maybe something to do with injector, fuel filter, that sort of thing? I'm no mechanic but I have always repaired my own vehicles so I don't think I'm too far off in my thinking. Ideas anyone?

[PINeely]

First step would be to swap the Cyl 3 coil with a different cylinder to see if the misfire follows it but since you already replaced the coil I think that's unlikely.

My bet is either spark plug or injector. Plug most likely but those old injectors are known faults with these cars. Pull the spark plug out and see what it looks like.

[Efthreeoh]

Originally Posted by PINeely

First step would be to swap the Cyl 3 coil with a different cylinder to see if the misfire follows it but since you already replaced the coil I think that's unlikely.

My bet is either spark plug or injector. Plug most likely but those old injectors are known faults with these cars. Pull the spark plug out and see what it looks like.

I think this is the correct diagnosis; the No. 3 fuel injector is going bad. A bad fuel injector will throw a P0303 misfire code. Had this exact same issue with my F150 just last week. New fuel injector solved the problem. Luckily the F150's injector is only $45 (but a PIA to replace!).

[matthatchett]

Sounds like I'm on the right path, thanks guys! I have 72k anyway so I'm going to go ahead and swap out all the plugs and then check into the injectors if that doesn't fix it. Thanks again.