Help - I think my C220 is possessed!
 

This is a very strange problem and I dont know where to start to diagnose this.

Car - 1994 C220 134K, bullet proof - never any problems

Problem first showed up last night as the radio and/or antenna not working, or would go on by itself. The radio goes on my its itself and cuts off randomly. Randomly the antenna goes up when the radio is on and randomly the antenna goes down - sometimes the radio is still on, but the antenna is down. I've noticed that if the car is on an forward? incline the radio is likely to more likely to come on. If I place the car in *drive* or *reverse* the radio is likely to come on.

The next morning i noticed the idle speed - normally this car idles at ~900rpm in neutral - now it's idling at ~600-700 rpm. which is normal for this car if the transmission is engaged, but not normal at idle.

Starting up this morning, the engine stumbled a lot and even cut out. It blip the gas for a sec, the engine stumbled for a sec before the computer readjusted.

Once warmed up, the car drove fine...shift fine etc.

I don't know if this is a concindence, but one of my rear brake lights fused during this whole morning episode.

I don't know if i have a check engine light yet - i still haven't replaced my airpump, so i'll have to pull the codes to see if any additional codes are trigger beyond the airpump code.

I checked out the OVP relay...I have the updated part and it's not fused. I have a brand new battery. Could it be the alternator causing this? volrage regulator? maybe a bad ground? (I don't even know where the grounds are on this car!)
a bad oxygen sensor causing bad idle?

Where do I start looking?

thanks,
chandra

I would suspect the alternator.

This model wouldn't be affected by the wiring harness issues like the 124's have, would it?

Larry - Yes, this is one of the models that suffers from the infamous MBZ wiring harness issue...but I have been keeping track of it and so far (fingers crossed) suffer from no wire degradation issues.

-Chandra

Update:

I did some voltage measurements and the battery is 12.75 voltage with the car off. With the car at idle the voltage is 17.50-17.75 volts!

I'm thinking it is the voltage regulator....where is this part located on the C220? I looked on the back of the alternator and couldn't see anything!

Thanks,
Chandra