Pulling hairs here
. My 135i decided to run rough 2-3 weeks ago after I took it to the drag races.. fuelled up with regular 94aki and added some octane booster to it.... it's now relegated as my week-ends car so i haven't had the time to put too much work into it until last week...
1) No codes
2) Everything is new or fairly recent; injectors rev12, plugs (OE bosch), coils ( delphi OE from M4)
3) Car was walnut blasted this week (valves where very dirty), but made no difference.
4) The car is FBO and push 25psi with ease
5) Noticed the valve cover is leaking in the spark plug area again.
6) The full tank has been used, now the car is back to the 91aki I have been using for years.
7) Idle reads about 16-18inHG, nothing unusual.
Only the idle is rough, above 1200-1300rpm everything is fine.
When using the bmw factory tools I can see that the cylinder #5 has a very high roughness measurement between 1.40 to 2.
No sure what to look out for next.