Hope someone can help...

First some background: 1994 Explorer 4WD, 4.0L V6. Recently replaced both O2 sensors and MAS for other problems which were fixed.

Here's the problem: on highway after approx 20-50 miles, it throws a Check Engine Light. Stays on for a couple of minutes, and then goes out, all through the trip. Last time was on a trip from Albuquerque to Santa Fe, which is a mostly uphill ride from about 5400 feet to about 7000(ish) feet. Had trouble staying at highway speed on the hills, but I don't know if that problem is related to the CEL. The truck has always seemed to throw CEL's after being on the highway for awhile, even at sea level. CEL was not in conjunction with any power loss, hesitation, etc, except what I'll call the "power loss at altitude" since I noticed it while driving cross country accross the mountains into NM when moving here.

On the way back, downhill, I only got a couple of CEL's, in 1 1/2 hours. (More than half a dozen on the way up.) When I got home, I threw the code reader on it. KOEO, no hard codes, but got memory codes of 124 (TPS voltage too high), 176 (O2 sensor bank #2 lean) and 177 (O2 sensor bank #2 rich). KOER, no codes thrown.

I found a test in the Tech Articles section about troubleshooting this code, which I tried to follow. The TPS check for voltage KOEO at 0 and full throttle was within limits. It next says to check the Air Charge Temp sensor. My Haynes manual doesn't list this sensor, so now I'm stuck.

Any help would be greatly appreciated. Sorry for the long detailed post, but I wanted to eliminate some possibilites. BTW, if anyone has ideas about my "power loss at altitude" problem, I'd appreciate that as well. Maybe vaccum?? I don't know.

Thanks in advance!
bob sends

 

Bob, when you tested the TPS did the voltage go from about 1v to 4v in a SMOOTH manner? A TPS can test good at both ends of the range, and still be bad. If it's shorted in the center portion, it'll give a "TPS voltage too high" code.....