I have a 96 z3 1.9 m44.
The car has had a rough idle since I bought it; Only 75,000 miles on it.
Cam position sensor
Front o2 sensor
Coil on plug conversion
New intake gaskets
Replaced vacuum lines going to injectors
Coolant temp sensor
Valve cover gasket (oil on plugs)
None of this fixed the problem, although the idle is 100% better now.
It still idles rough and began hesitating while cold. I'm considering a new maf, crank position sensor, throttle position sensor and possibly idle control valve.
I've been advised a fuel pressure regulator could be the cause also.
I pulled the lower intake apart the other day to see what's going on. I found black gunk on the ends of the injectors as well as all inside of the intake where the injectors go. It was also on the intake valves, this came off easily with carb cleaner and degreaser. The car ran horribly until I revved it for a minute, I guess it had to work out the cleaner.
Anyone have any insight on this?