I agree with rick. My 85 300SD has a vacuum pump in the trunk. I don't know how reliable this is, but those Key lock really take a beat'n so I would not discard another suspect just yet. I was having problem with my car not shutting off. I looked at the vaccum pump, I removed the ignition vacuum diaphram....Nothing. Guess what...three rubber diaphrams that control the flaps for a/c ducts were busted. Well, as soon as I replaced them, the car started shutting off immediatley, Plus, my tranny started shiftting smoother. Better take a look around to see if one of your diaphrams is busted!!! If you are having problems with a/c controls and air directed in the wrong way...BINGO!
