Hi, new owner of a 91 740 SE Turbo Wagon with 180K miles.
My wife drives the Wagon every day with the lights on (no matter what time of the day). Recently, she complained that when she came to a stop sign, the RPM acted erratically and the engine almost die. I drove the car for a week trying to replicate the problem and nothing. The last day I drove it, with the lights on, the RPM acted erratically suddenly everything was back to normal. I am not sure if this occurs only with the lights on or not.