A search of the forum shows multiple posts on the issue of blower motor/hvac issues, but I haven't found a post describing what I'm experiencing. My 1988 190D has suddenly started displaying an erratic blower motor. Turn the system on and the blower will come on, then drop out, then come on, then drop out, etc... The odd thing is, every time it kicks in, the engine idle drops, so along with the blower surge I'm getting an idle surge. At first I thought it was my imagination, but not so. Has anyone ever experienced this? Is it indicative of a failed or failing porcupine relay? Or is it possible that the brushes on the blower are just about to fail and it's powering up, losing contact, powering down, regaining contact, etc? The ignition switch has always displayed a tendency for poor contact in position II. Since I've owned the car it's been normal to have to just slightly twist the key to retain/regain contact. Fiddling with the switch doesn't effect the issue, but ... ? I'll start the process of checking for burnt fuses, etc., but thought I'd ask first. Thanks.

Just to answer my own question, and since nobody replied perhaps this will help someone else: The problem was a worn out blower motor. Removing the motor, which was not making any untoward noises, revealed a very stiff motor shaft. Apparently, it was pulling huge amps when it energized. That in turn caused the protection circuit in the blower motor relay/resister unit to shut off the blower as it was drawing too high a load. It would then stabilize, resume power, draw high, repeat. A new blower motor and it's all working perfectly. Easy job, too.