Hey all, I've owned this car for a couple months and it's been a blast. I've been driving it pretty hard in the hill country here, hitting the "Sport" button is a habit when I start the car every day. Last week, under hard acceleration, it backfired between gears. At the next light, the engine was running very rough. The idle had a hiccup and now it sounds to be running on 3 cylinders most of the time. The car has 65K on it now, there is heavy stuttering and random backfires at idle, and it does not sound healthy if I apply the throttle. I added a bottle of Techron fuel additive to see if I could remedy bad gas or maybe a dirty injector, but it has seemed to only get worse. Once the engine has warmed up, the stuttering is minimal, but it still happens. I've avoided driving it until I can track down the issue, hopefully someone here can give me some insight. I've ordered a new set of NGK iridium plugs, should be delivered today. Any clue?

EDIT: Here's a video. I had let it warm up a little and went back out an hour later to shoot this clip. I've been running straight pipe from the secondary cat back, would this have caused major issues?


EDIT 2: Replaced the spark plugs with the NGK iridiums. The car is plenty warm since I ran a mile down the road to Autozone for a part. It idles just fine, but still feeling a little choppy while in low RPM. Would that be caused by the ECU trying to manage the misfiring? I threw the code P0301

 

I believe this is the wrong section for this, but not sure as I'm a new member as well. I'm actually chasing a similar problem, but with cylinders 1 and 3. Based on some brief research, I believe the coils are the culprit. Planning to replace the coils and spark plugs, will advise once completed.

Regards,
EMNI

 

I will add that replacing the spark plugs has vastly improved the engine performance, but anything over 1/3 throttle and the engine will stutter heavily.

 

I always hate finding a thread that doesn't have an answer, so here's my fix!

P0301 was a misfire on cylinder 1, I went ahead and replaced all the spark plugs at 65K miles and it helped but was still stumbling/backfiring at 1/3 throttle. A new ignition coil on cylinder 1 was all it took to get the car running great again. I noticed the one I pulled was a Delphi unit, not sure who manufactures the OEM coils.

 

Delphi seems to be OEM. Not high quality at all, thanks bmw

 

My check engine light came on this morning and the engine would sputter when trying to accelerate. Codes indicate bad ignition coils and spark plugs. Having them replaced at 40K miles.