Pontiac Repair: p0420 code, p0420 code, threshold bank

Question
QUESTION: My sons 1997 Firebird 3800 MILEAGE AROUND 160000 was spitting G and sputter and shaking the would choke off. We took to dealer they said without a doubt it was a bad ignition module a$600 repair job. Couldn't handle that now so we had CAR TOWED HOME AND PURCHASED MODULE AND INSTALLED, CAR RAN GREAT FIRST 5 MILES OR SO THEN STARTED SPITTING AND SPUTTER AGAIN NOT CHOKING OFF NOT RUNNING AS BAD CAR HAD BEEN SITTING SEVERAL MONTHS WITH1/4 TANK GAS SO I FILLED AND USED SEAFOAM NOW CAR IS RUNNING OK STILL REVS A LITTLE WHEN IDLE BUT CHECK ENGINE LIGHT IS BACK ON AND DUE FOR INSPECTION CAT. CONVERTER AND O2SENSOR BEHIND CAT CONVERTER HAS BEEN REPLACED COIL PACKS REPLACED CAR MAINLY REVS WHILE IDLING LIKE YOU ARE TAPPING THE GAS PEDAL GIVING ME A CODE PO420. I THOUGHT MAYBE THE O2 SENSORS I UNDERSTAND IT HAS 3 I CAN ONLY LOCATE 2 ONE BEHIND CAT (REPLACED) ONE VISIBLE FROM DRIVERS SIDE IF LOOKING UNDER CAR. WHAT DO YOU SUGGEST?

ANSWER: what engine is in this car? A 3400 V6? did you have the car scanned for codes right now after the module was replaced? if so what is the code for? As far as a erratic idle I would clean the throttle plate and throttel body bore along with the idle control motor. disconnect the battery let it sit for a while and reconnect the battery. then do this. turn the key on but don't start it wait 30 seconds turn the key off wait 30 seconds. turn it on and then off agian each for 30 second intervals and then start the car see what happens. If that doesn't fix it I would start looking for a vacuum leak that will amke the idle do strange things as well. The problem is with that kind of mialge on the car it could be just about anything. Good luck :)


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QUESTION: THE CAR HAS A V6 3800. THE CURRENT CODE SINCE MODULE WAS REPLACED IS P0420  CATALYST EFFICIENCY BELOW THRESHOLD BANK 1 BEST I CAN TELL THAT IS LEFT BANK O2 SENSOR BUT I CAN'T FIGURE OUT WHERE LEFT BANK SENSOR IS?

ANSWER: The left bank "1" is on the driver side of the car. That car should have (3) o2 sensors one behind the converter and one in each manifold. It's very rare for an o2 sensor to cause a p0420 code that code is usually cause by a high milage car or one that was misfiring for a long period of time. I have seen a few o2 sensors cause this but really rare.. I would have the o2 sensor acativity verified with a scan tool before I go any further... The erratic idle you are talking about could affect the converter as well...


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QUESTION: ARE YOU SAYING THE MILAGE ITSELF COULD CAUSE THIS CODE AND IF SO IS THERE NO FIX FOR IT IT IS DUE FOR EMMISSIONS INSPECTION THIS MONTH. ALSO I'VE LOOKED ON DRIVERS SIDE I ONLY SEE 2 SENSORS ONE BEHIND CAT ONE IN FRONT OF CAT ON INSIDE OF EXHAUST ON PASSENGER SIDE.  THE DEALER SAID THE ignition module WAS THE ONLY THING THEY COULD FIN

Answer
I just looked. that engine actually has 4 o2 sensors. 1 in each exhaust manifold and 1 behind each cat converter. what I meant was when cars get a pile of miles on them thye converts just wear out. the other reason for failure is an engine misfire meaning the engine is misfiring and the raw fule is sent into the converter. Wich sounds like what happend here the misfire damaged the converter. if that p0420 is stored in the computer the converter is bad. if you put an aftermarket converter on this that bcan cause the code to come on as well. like I said you need to see what the 02 data looks like before you start condeming anything. but if you don't fix the running problem or misfire you will damage a converter again.