My '89 535 is difficult to start at first. Then when it starts it runs rough and I can smell gas. Then the idle will even out. But then after idling fine for about 2 minutes it starts to run rough again and I there is a "rich" smell coming from the exhaust and you can see that the tailpipes are blackend. Here is what I have done so far to try and fix the problem:
1. Installed the inline "check valve" at the fuel pump.
2. New oxygen sensor
3. New exhaust
4. New Plug wires, Cap and rotor.
5. New Coolant temp switch
6. New Spark Plugs
7. Six new Injectors and O-Rings.
8. Cleaned Idle Control valve.
9 Check computer and no fault codes are stored.
Could it possibly be the fuel pump, idle control valve or fuel pressure regulator? The pump does make a loud buzzing noise, but I cannot see how that could make things run rich. Any help anyone can give me would be much appreciated! Thanks!