About a month ago I was throwing a CEL which came up being my TPS so I played around with a few things and reset the ECU more than a few times then the CEL never returned and I had nothing stored in the computer but my MPGs are continuing to plummet. My mechanic checked the voltage reading on all my sensors and everything came back normal including my TPS and he didn't want to put on new parts if the old parts weren't really bad.

Could the bad TPS still give proper readings but still be a problem or could it be something else me and my mechanic are overlooking? Mine is a Cali emissions truck so could the A/F sensor cause some issues but the O2 sesor not be a problem?

My last resort is take it to Toyota to figure it out and pay throught the nose.