I have an '89 240 that has been running rich since I bought it. I tested everything I could and replaced the ECU. I also upgraded the ecu from a pink label 561 to a 951. This helped a (very) short time, and then back to running badly. I took it to a reputable shop and they went through it with a fine-tooth comb, including switching out various components, including ecu, which they said was the problem. I bought one from a respected member here and it ran good for a (very) short time, now back to running like
c%#$!

Now the question: Can there be something in a component, or the wiring harness, that is screwing up the ECU and keeping the car from running correctly? The problems are that it is very cold-blooded, smokes black, idles too low and dies.

I did have another thought, probably due to lack of knowledge: The car, I believe, had just had the timing belt replaced before I bought it, having sat for a year or two before this. Could the timing belt have been replaced one cog off and be causing the same thing?

Help, I'm getting deperate here. It's a good car otherwise, burns no oil and is straight and rust free. THANKS!

Jeff