It started last year I took it in and they said the code was indicating a lean mixture but they could not reproduce the prolem. They reset the light and it was fine until a few mnonths ago. This time it cam up as a lean mixture code and an evaportive emissions code but again they could not reproduce the problems. In the past few months when I went to go start the car after it has been sitting overnight or for several hours it would hesitate when I hit bthe gas(like it wants to stall) and after a few seconds it would run fine. Occasionally it would stall and then when restarted it would run fine. Sometimes when getting on a highway it would seem to not have enoughh power after 35-40 mph and then it would begin to accelerate after a few minutes.
Check engine light on 2001 Toyota Corolla
by JayL in Englishtown, NJ on July 04, 2010
ANSWER by tarheel007 , July 09, 2011
If the code that came up was PO171 (lean mixture bank 1), it might be a bad O2 sensor, dirty/bad MAF sensor, vacuum leak, vs other. The problem on my 2001 corolla was that when I first started, when you hit the accelerator, there was hesitation but then was fine until you had to restart the car again. Try cleaning the MAF sensor (pretty easy to do, it is right at the level of the air filter body and held on with two phillips screws). The cleaner you can buy at an autoparts store (CRC mass air flow sensor cleaner) for about 6-7 bucks.