its been throwing a po 420 code bank 1 (catalyst efficiency below threshold) on and off for a month or so... never had any problem with it tho... figured i might've had a bad cat... have it replaced under warranty (80,000 miles for cats) or whatever

yesterday, light was on all day... car was running fine. then i throw a 5 gallons of 101 unleaded in it to go to the track on (mixed with about 2-3 gallons of 91 that was already in the tank) and it still runs fine... lights still on... i stop at a gas station to take a whiz, come back to the car... start it... runs for a second and dies... did this like 3-4 times in a row... then everytime i tried changing gear from D to R etc... i probably had to restart the car about 8 times to get it out of the gas station parking lot, then for another mile or so i just kept it stalled up to about a 1,000 rpm at stop lights and such.. (the light has since been off this whole time by the way) then, i get on the highway, cars running fine... get to the track... no more stalling problem, idles a little low and inconsistant... but its not wanting to die.

im thinking, bad front, bank 1 o2 sensor? exagerated by the race gas?

 

anybody?

im lookin for input here fellas

 

Have the code(s) pulled again, and see if there are any new ones. The PO420 can be caused by:

Exhaust leak(s) which can hide a degraded catalyst or cause a false ses.
Fuel contamination.
Use of alternate fuels.

 

Well I would say since it's warrantied just go to the dealer and have it taken care of.

 

the cars not under warranty..

i was talking about the cats

cats are warranteed (federally mandated) until 8 year/80,000 miles


but its obviously not the cats.

 

It's your O2 sensor. It gave you warning and you did not heed it. So now it is saying "screw you" and causing you idling issues. Pay attention to your gas mileage, it should be getting worse also.