Thanks M5

The car: 1989 535iA 126,000 miles

The symptoms: Happens mostly at idle (about 700 rpm). Warm or cold. The engine will start to stall, rpm dropping off, and then will surge momentarily to about 1100 rpm and then settle back to 700 rpm. Sometimes it will completely stall. I can usually prevent this surge/stall by slightly stepping on the accelerator.
There appears to be no regular pattern when this happens except maybe when slowing quickly.

Recently was running about 110 MPH and for first time the engine started missing. Not bad but missing just the same. 80 MPH no problem

I've replaced the distributor and rotor, new plugs, new ICV valve, tested the AFM, ECT sensor, TPS, CPS, spark plug wires using the methods/values from Bentleys. All resistances/continuity were normal. Adjusted valves and added the improved banjo bolts.

The CPS was covered with gunk and I clean it off but not sure if I did a through job of it. I will revisit that job soon. Also checked for air/vacuum leaks, did not find any but am considering getting all new hoses in case there is something I am not seeing.

I have tried running the engine and wiggling the sensor wires from the different ones looking for an intermittent ground/short. Have not done a complete job of it and will look at that again.

I check the ignition coil. Can’t remember exact readings but they were around 9,000 ohms (slightly high) and less then 100 ohms (way low but can’t believe that is the problem).

Have not checked the O2 sensor yet, but it has less then 20,000 miles on it.

I'm thinking it could be a fuel problem. Will be checking the pressure(s) in the next day or so.

Jim