OVP + IACV problem, with bad idling!

[Unleashed]

I used to have a problem where if my IACV was plugged in, the car would just stall as soon as it starts. I thought I had fixed it when I replaced the water temp sensor (4 pin).
I knew my OVP relay was gone, so I replaced it today. The above problem has come back. The only way I can make the car stay running is to unplug the IACV.

The other problem I have is bad idle:

1) At cold it idles really low, as it warms it raises until it evens out at 1000rpm.

2) When I put it in gear it drops 400 or even more revs! As I understand it, it should only lose about 50?! It runs like crap when I'm sitting in traffic idling at ~500rpm and it constantly feels like it's going to cut out.

1989 190E 2.5-16v.

Please help. This is driving me nuts!

I'm posting this on every car forum I'm on in the hope that someone has had the same thing and can point me in the right direction.