Originally Posted by AceEngineer

I finally fixed my rough idle and miss problem with my E83. For some time I have had a rough idle and lately a consistent code for a miss in cylinder 4. I switched the coils and put in a new plug but it still gave the #4 miss code. My next thought was it must be the injector. After two tanks with injector cleaner and no results I just decided to replace all the injectors (130k miles). Once we got the fuel rail out, my son climbed up and looked straight down all the injector holes and announced that the #4 looked different, it was black at the bottom instead of metallic aluminum like the others. Went to a buddies and borrowed a borescope. When we looked in we could see something obstructing the intake runner. The picture was clear enough that we could make out a waffle pattern on the blockage and see the valve stem it was resting against. Looks just like the pictures of a DISA valve flapper. Soooo.... pulled the intake manifold, removed the DISA valves and sure enough the outer DISA valve was missing half its flapper. Fished the piece out of the intake runner and replaced both DISA valves. Wow, car runs much better, even seems to have more power and now a smooth idle.
FYI: new injectors $300 ($50 each) and DISA valves $430 for both.

AceEngineer