What would cause a BMW 3 series E90 to misfire until the engine has warmed up?

Question

I took my car to a mechanic because of misfiring issues. He said his computer told him it was an ignition coil pack issue, specifically coil 1.

Anyway, he changed it and the car was still misfiring. I also noticed, prior to taking the car to him, that I'd have to wait for the car to warm up, and only after it warmed up would it not misfire. The engine management light would also stop turning on and off.

If I tried to drive the car without letting it warm up, it would jerk and misfire, and sometimes the engine would cut off if I revved too lightly.

To cut a long story short, the mechanic said I should replace the car because fixing this issue would cost too much (£900+) and it wouldn't be worth it. He said something about having to remove seats and so on, to diagnose the problem. However, I have a gut feeling he's just not experienced enough to deal with this kind of issue.

My BMW is a 2007 E90 M-Sport (Petrol). I've owned it for about 5 years. I don't really want to buy another car unless I really have to. I'd like to find out what the possible problem could be, so I know exactly what to say when I get a second opinion from another mechanic. At least if I show up having some knowledge, the new mechanic will realise I've done my homework and take me more seriously.

I have my notepad ready and I'm looking forward to any suggestions advice any of you can give me.

Thanks in advance.

Answer 1

I’m probably waaay too late to this party, but I thought I’d chime in. The E90s are a bit of a paradox, much more reliable than the E92s and above, but the start of the end for our beloved Bavarian Bimmers.

The E90s’ N43/44/45 and N52/53/54/55 engines have an issue all owners should be aware of, faulty ignition coils. The engines run like a dream, up to about 100,000 - 150,000 kilometers. Once they go, the most common symptoms include loss of power, misfiring and long warm-ups from a cold start. This happened to my N52 3.0 right at the 100,000 kilometer mark. Good news is that my mechanic was able to identify the problem and with input from both the OBD II port (under the dash) and explicit information I gave him about drive feel, sounds and car behavior, he found exactly what the problem was without too much problem. I asked him to go the extra mile and replace the entire IC pack as well as the plugs to be safe. Haven’t had the problem since.

Diagnosing the problem DID NOT require removing anything fixed like seats or wheels or doors anything as daft as that. Anybody who says it does is an utter numpty. Most problems can be identified through the Onboard Diagnostic port (OBD), information from the driver and a bit of experience. I’d agree with going to the dealership, but dealerships tend to be pricey (especially since your car is well past warranty). Find a new mechanic, someone who specializes in German cars. You can tell if a mechanic does specialize either just from the advertising or by simply visiting his garage and taking a look at the cars in his queue. If his queue is full of Bimmers, Mercs, Porsches and VDubs, you’re in good hands.

I hope this helps you next time this happens and that you didn’t buy a new car to replace that M monster.

Removing seats for a Diagnosis... Some people!