I'm having some engine performance problems on my 1987 745. The car is new to me and I'm trying to work out the bugs. 1) When I start the car (often when hot, but occationally when cold) it takes about 20 seconds for the engine to run clearly. In this first 20 seconds it idles smoothly, but if I try to take off - it coughs and hesitates. 2) When running at speed it will infrequently (once every 5-20 minutes) hesitate slightly. Also, at times the engine does not feel like it is running at full strength.
The other day I noticed that when I turned on the headlights it did the exact hesitation that I mentioned above. Then I turned them off and it did it again. Since then I've done this several times - and it is quite consistent the first time I do it - especially turning the lights off.

Both the previous mechanic and my mechanic have checked into the likely suspects. To my knowledge: AMM, throttle body, fuel pressure regulator, flame trap, oxygen sensor, cleaned fuel injection, and tested for leaky fuel injectors.