Temperature Problem

[PMStaples at aol.com]

I have a 1988, 90 Quattro that does not want to run at a certain temperatue. 
When it is cold it runs fine, then as it begins to warm up, usually by the 
time I leave the house and get into traffic. It stumbles and misses badly, 
almost dying. I am forced to give it full throttle to bet the thing moving, 
which has not been doing my new clutch any favors. After it warms up, maybe 
just a couple of blocks later, it runs fine. Stop the car for 15 minutes and 
the whole thing starts over. I checked the error codes and got inconclusive 
results like WOT, which tested OK with my meter and replace the ECM.
Spring is coming, and the problem might go away for a few months, moning 
south would help, but I am stuck here in the Midwest.
Any suggestions will be appreciated.
P.M. Staples