I have had a new 93 for almost a year now, and I have been having running rich, cold start problems intermittantly since I got it. I have replaced or swapped in known good power stage, cps, temperature sensor, and oxygen sensor.
The error codes have always been for the temp sensor, and compensating for lean/rich fuel mixture. The check engine light never came on (it should have) but I later discovered that the previous owner had smashed the warning bulb.

At first I thought it was the ecu and swapped in a 942 ( the EGR one). It worked OK until the check engine light came on again. Error code was for temp sensor. I replaced the temp sensor, and also swapped in the known working 561 from my 89 in case it was the 942. That was six months ago and the car has worked great. The 93s original 951 ended up in my 89 and the car has worked normally, so I figured it was the temp sensor the whole time.

So today I tried putting the 951 back in my 93. Same problem as before. All I could smell is gas and the car would barely run. Swap back in the pink label 561 and the car runs fine. I put the 951 back in my 89 and it runs fine.

I'm not sure what to do. I am selling the 89, and I don't really want to let it go with the supposidly more reliable 951. Any suggestions?