I have a 90 740Ti.

Once every couple of months since November, my car has started acting funny while I'm driving home. It's been at night both times.

I'll be driving along or slowing down and the car starts feeling like it has a huge pre-ignition or misfire. It's irregular. It happens more than 10 seconds apart, but in bursts and usually is fine for 30 seconds, then does it a couple times, then is okay.

It's not a trans problem - rather, the miss happens in park and neutral.

I have a similar miss at idle. Once every 15-30 seconds, I will have a single sputter and the car runs ok. Power, etc is good, but my mileage isn't great.

Tonight, I pulled over, checked the belts to make sure none were seizing. I checked the coolant and checked the oil the day before - both fine.
I disconnected the AMM and the engine revved up, but still had the miss. It happens at all rpms. I checked the FPR - it seemed fine, no fumes or drips. I shut off the car, and only got the AMM disconnected code (LH2.4: 1-2-1). I opened the air box to make sure that wasn't it (after turning it off). I restarted and the problem didn't recur.

I think the problem is injection related. The ballast resistors are old (I don't really understand their purpose, can someone explain? is it just to prevent from overvolting the injectors?). The injectors aren't new, don't have new seals, etc.

I do need to have my timing belt and rear cam seal replaced soon. My mechanic will do the distributor cap and rotor at the same time.

plugs, wires, filters, etc. are all pretty recent.

Any help is appreciated.

-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond