I have a 1985 318i and as of late it has been acting wierd. While I am driving the tach will suddenly begin to act possessed and jump around like crazy and it sounds like the engine runs a little rough, but not horribly so. If i floor it the tach catches and its ok for a while. If I dont see it and let it go, the stereo goes dead and possibly the headlights, but I dont remember. If the stereo and fan and everything are turned off it is less likely to do it. My only guess is the alternator or some sort of voltage regulator or something like that. Does this sound familiar to anyone??