A couple of weeks ago, the check engine light (code P0420 – Catalytic converter efficiency below threshold) came on our 2002 Corolla. After the catalytic converter and the O2 sensors (both) were replaced (as suggested at the mechanic shop) the car has been stalling intermittently. If we were to idle at a stop light for 3 or 4 minutes and then try to go, it would stall/hesitate to go forward for 2-5 seconds and then take off as I give more gas to it. This never happened before or even when the check engine light came on (before the repair)
After a visit to the mechanic shop, they suggested changing out the Mass Air Flow sensor as it seemed to be most often cited cause for this problem. After this change, the car seemed to run fine for a couple of days and now it’s back again with a new check engine code – P0133 – O2 sensor circuit slow response – Bank 1 sensor 1.
Took it to the shop again and after leaving the car overnight, they swear they can’t replicate the issue. I asked them if it could be a problem with the sticky throttle or dirty throttle body and they said they cleaned it out. They ended up changing the Mass Air Flow sensor again as it seemed to fix the issue (for 2 days) previously. I’m feel the problem is not fixed yet and sooner or later the “stalling/hesitation” is going to come back with or without a check engine light.
I’m lost as to what the problem is and if the mechanic shop is failing to look at something or not accepting their fault when they changed out the catalytic converter. I would greatly appreciate if someone would respond to this question and let me know if there is something that I can do myself to diagnose the issue.
Thanks in advance!