I think its throwing this code because i have no catalytic converter. but it wasnt throwing the code when i got the car. when its hot it dosnt run well. when i start it sometimes it will turn right back off. and when im getting up to speed barley on the gas it will stutter and not want to go but if i floor it. it wont stutter. any ideas?

 

check your 02 sensor to see if its fouled. may want to get a simulator to replace the rear 02 sensor or have them tuned out.

 

what does fouled mean?

 

covered in black, should be clean with a light brownish sorta color.

 

ok thanks man ill check that tomorrow

 

The PO420 is referring to poor catalytic converter performance, which is read by the post-cat O2 sensor. With no cat, someone must have already installed a simulator, or used the spark plug extension trick to fool the system, or tuned it out of the PCM as craby mentioned. If the stock post-cat O2 sensor was left as factory installed, it would have tripped the code right away.