After resting my hopes on fixing a bad connector my 1990 240 wagon still runs rich, idles rough, and sets off the same codes.

I spliced in the used connector Tom Coffey, parts specialist at Don Beyer Volvo - Sterling, clipped off an old harnass. I noticed great improvement for a period/distance long enough for me to think this fixed the problem. When Tom gave me the connector he said he hoped it would be the cure, but that he regretted to tell me that he thought it might be the ECU (because the car would run best after disconnecting the battery...not simply resetting codes). I still had hope for the ECT connector fix.

I replaced the ECT sensor last week (after the FPR it was the next logical culprit). Last night I checked the old sensor's resistance after sticking the sensor tip in boiling water. Perfectly good sensor....nice steady increase in resistance as the sensor cooled to room temp, all within specs.

I have not checked the ECT resistance at the ECU connector, as Art suggested. I tried to last night, but I don't know how to identify pin sockets #13 and 5 (if these are correct). I have the infamous pink-labeled ECU 561. It's amazing it lasted 14 years.

I'm picking up a new ECU 951 later today at Don Beyer. It's expensive, but not as outrageous as some I've seen online for cars with EGR....and I never found a new #951 online (only 571, 556, and 933). So far every ellimination has pointed more and more to the ECU. When I searched the archives and 200 forum I found lots of similar problems with the ECU 561 (there's one on ebay and the bids are very low....which says a lot).

Tom Coffey mentioned something else of interest. He said he's heard people say jump starting the car (or another car) can send a current spike that kills the ECU. This is interesting because the first time the engine light came on it indicated the 02 sensor (which I replaced, but the car was still running fine with the old sensor)....However, I jump started a friend's car at work a few weeks later. The check engine light came on immediately. I've had the running rich, stumbling idle ever since. What I thought was a single check engine light issue seems to be two separate problems. First the 02 sensor, which I fixed. Then jumping another car and frying my computer (I hope the #951 ECU is better protected). If several months had passed between engine light episodes I probably would have realized they were unrelated.

Jon