I have a 1984 533i that is not holding idel. Once warn the engine goes into the strange cycle where it revs up to 1700 rpm and then back down to 1000 rpm and just keep going, back and forth as if it's searching for a corect idel rate. I can't afford to have a mechanic work on it. I know how to fix things, but this puzzels me to no end. any pointers from you BMW guys? I think it's vacuume related.