The infamous "cold start" misfire E46 325ti

[wnw65]

220000km on the clock and still going strong, that is besides the odd cold start misfire. Scan codes reveal misfire on bank 1 and related ignition coil fault and O2 sensor control limit. As a precaution I check for air leaks on the intake side of the motor. Blow me over. That elbow connecting to idle control unit on the lower intake pipe. Stuck my finger right into it. Yippee fault found. Stripped it all and got replacement from stealer. But had to wait a day to get it ordered and delivered. So cleaned ICV and inspected MAF. Ah another leak, the breather pipe between oil separator and dip stick. Remove and replace. Cool, put everything back together and clear codes. Motor starts first time, nice and smooth. Go for a drive. All good.
Later go to school to fetch kids. Boom, misfire. This time bank 2. Pull ignition coils and found water in 4 5 and 6. It had rained the night I had everything stripped off. The water ran in through the bonnet vent and filed the spark plug holes.
Hope this lesson makes my wiser.
Cheers

 

[Philip Foglar]

Do you ever start the car from cold just to move it out of your garage, for instance to get to something that is otherwise inaccessible, and then simply bring it back in again? My Wife did that once before and when she started it the next time the engine had a nasty missfire which did not go away even after driving for a bit. She brought the car back so that I could take a look, but after we started it up again it was fine. The condensation causes sulphuric acid and carbon layer in the combustion chambers which could very well cause this missfire and then confuse the ECU I suspect, that is until started again. So for this reason, none of the cars ever get treated like this - even if it mean having to take the car for a drive just to get to that dammm box! :rollsmile:

 

[wnw65]

I use the car daily. Do at least 20km. Odd thing though, never did it when i left work in the afternoons. Mornings only. Hence my assumption of "cold" start. But it has been fine since the repairs. I ran it to Hermanus and back today. 220km round trip. Averaged 8 L/100km. All I have to do now is sort VANOS issue it would seem. "Lag" below 2000rpm.

 

[Philip Foglar]

Have you tried pulling those suspect coils one at a time while the engine is running to see if there is any difference to the way the engine idles - in other words, if one of them is pulled and there seems to be no noticeable difference, then chances are that one is a faulty coil.

What about things like, running a tank with a good injector cleaner?

Not sure what else could be doing this, and you have already ruled quite a few things out...