The "check engine" light just came on today during the drive home. I pulled over, checked for any obvious loose wires, etc, but found nothing. I used the diagnostic connector and found that it gave me a 2-3-1 code, which supposedly means "fuel system compensating for rich or lean mixture at cruise". I cleared the code and restarted the engine, but the "check engine" light stayed on. The car seemed to drive normally, no loss of power or acceleration, and the temp gauge stayed at its normal position. The car is '89 240 wagon, automatic, with about 210,000 miles showing. I've owned it for the last 40,000 or so, it passed the emissions test about 6 weeks ago with completely normal numbers, and the O2 sensor was replaced about 10,000 miles ago. Any suggestions what I should check next?
m9876c at yahoo dot com
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some additional information....
Checked all wires and hoses, everything seems secure and intact. Measured the AMM heater pins, correct resistance. SAme with the O2 sensor heater. From past experience, I know that if the AMM is disconnected, the car is almost impossible to start, yet this morning it started easily when cold, and ran fine last nite on the way home. Granted, that's not a guarantee that the AMM and O2 sensor are good, but it seems to clear them of blame for now.
The manual mentioned "low fuel pressure" as a cause. Both pumps and the filters were replaced about 1.5 years ago, and if that were the problem now, I'd expect to have lost power on acceleration last nite, which didn't happen, even when going uphill. Similarly, if there was a fuel delivery problem, like a failed injector, I would have noticed the loss of power. Same with ignition (Plugs and wires changed a few thousand miles ago)
I cleared the 2-3-1 code this morning before the cold start, and the "check engine" light never went off after starting the engine. Seems that if it was actually sensing a rich or lean situation (say, from a stuck injector), it would have taken a few minutes for the system to realize it, so the light should have gone off and come back on later.
Any other suggestions?... Car is perfectly drivable, I just don't want to damage anything if it can be avoided.