1984 190D inconsistent idle problem
 

Hey guys, the car in question is my 1984 190D with 2.2L and auto trans. Got the car for free about a year and a half ago (and we all know that you get exactly what you pay for). All in all, I've been tackling issues one by one and making a decent daily driver. One of the last issues I'm dealing with is a wierd idle problem...here's the deal.

FYI:
-Tach doesn't work, so all engine speed estimations will be just that. (Anyone with suggestions on getting this going is welcome!)
-As a point of reference, I've owned two other 1984 190Ds so I think I have a fair idea of normal engine idle speeds.
-Car's electrical system was seriously hacked by previous owner, keep this in mind if there is an electrical system to control my complaints.

Car idles very low when cold or when hot with AC compressor engaged. If I turn up the idle with the throttle cable to allow for normal idling under these conditions, the hot idle goes through the roof. Likewise, if I turn down the idle with the cable to allow for normal hot idling, cold idling or turning on the AC will actually idle the car down so far it will shut off.

I have tried adjusting idle speeds with the cable as mentioned and have found a range that is workable, but not right. I have read on these forums about an ELR although I don't know what it is, nor can I locate it on my car from the information I found on the forums.

Thanks to anyone taking the time to read this and share their experience with me!
Brad

Check OVP (over voltage protection relay). You can find it behind the battery, remove the plastic covers. It is a metallic gray with a fuse on top. Even if the fuse is fine, I'm 90% sure it is that the culprit.