I've 318i for over 2 years now. 2002 model and about 85k mileage. Just recently it started misfiring.
I took it to local bmw service centre and on diagnostics it was "Misfiring found in all cylinders summation error" along with "misfiring found in cylinder 1,2,3,4" randomly.
Detail Diagnostics As Suggested by BMW Service:
Costed me £80, coils, plugs were fine. They said its breather valve which needs changing after 60k anyway.
Breather Valve Changed:
Costed about £340 and after a day of run I noticed problem was still there. Took it back to bmw service and this time they said its faulty Air Mass Meter which had a knock on effect.
Air Mass Meter Changed:
Costed about £200. Bosche like for like replacement and you know what, It still misfires :(.
Help pleaseeeeeeee !