[thom4782]

Thanks everyone for the advice so far.

After the last round in the shop, the CEL popped back on the first start after 50 miles. All the secondary air parts have been replaced now. So I am beginning to think its one of the O2 sensors. Two questions. First, with a 91K car, can an oxygen sensor be bad without throwing any of the codes. In all time, no O2 code has ever been seen although the mechanic once mentioned a sensor was slow to react. Not sure how he knew this. If yes, is there any way to tell which sensor may be bad? Second, is it true that after resetting the codes, the car's computer waits for 50 miles until it checks again for CEL related codes. Thanks