My '87 740 GLE 280,000km has started acting up. It occurs when the engine is warm, at idle, in drive with my foot on the brake. Idle drops to almost stall, sometimes stalls and sometimes drops and surges high (causes the car to jump ahead if the brake is not on firmly). Throttle body has been cleaned, IAC cleaned, and flips from stop to stop freely. Grounding test point drops the idle, surges up when it is ungrounded. I can adjust the idle with the black adjustor (when test point grounded) to stall, but not much above 800 with the adjuster backed out all the way. New cap and rotor, wires and bosch platinum plugs new about 10,000 km ago. The connector on the hall sensor on the distributor was broken when I changed the rotor, and I put it back and it is held in place with the new rotor, but the problem started just before I changed the cap and rotor. I have removed the power stage, cleaned it and put thermal grease between it and the alum. block. All plugs to AMM, IAC, power stage, etc have been cleaned and dielectric-greased.
Any suggestions? Idle is good when the motor is cold. Not sure where to look now. I just fixed a bunch of stuff, now this. Do your cars ever run nicely for a good 3 month stretch without something popping up?
thanks