Replaced the precat o2 sensor cuz I kept getting the same check engine code0420 and now it runs like crap.any idea what would give it a code for a lean condition?so far I had to choke the air down on the cai to smooth out the idle.thanks

 

plugged or failing injector can cause lean condition.

 

An oiled MAF wire that isn't reading properly, that came from an over-oiled CAI filter...

 

ok here is a list of thing ive done.cai and headers.car ran normal with bank 2 o2 sensor inefficiancy so i did the sparkplug nofowler trick and got rid of that code.then i got a o2 bank 3 just before the cat and replaced that 02 sensor and as soon as i did that the car would idle up and down and just run like crap or stall out?so then i choked the amount of air at the cai so it would smooth out the idle.but this was ok before so i undone that and put it back the way it was and it ran like crap.then for whatever reason i unplugged the mass airflow sensor and it smoothed out and runs great.i tried a difff maf sensor but it didnt help me so im looking for some ideas or help cuz this has taken some fuel economy away where before with the cai and headers i got really good milage still.thanks for any help on this.oh and i had a chip that piggybacked the mass airflow sensor but tookm that off cuz it was a joke but hope it didnt mess up my pcm any?thanks

 

what kind of 02 sensors did you get, bosch dont like my motor. in any case you could have gotten a bad 02 sensor. you can clear the computer by unhooking both battery cables and connecting them to eash other for like 10 minutes to ground out and reset the system. do not touch them together while hooked up to battery. it will take a few starts for the computer to re learn so it may run rich a while

 

Thanks I will try that in the morning.i think it was an ngk o2 sensor but not certain.i have the box it came in outside but I know it's not a bosh.

 

new headers can have a coating on the inside that can foul the 02 sensors while the stuff is burning off.