Ok i've sifted through alot of threads looking for the answer to my problem...i've read anything from bad cats, bad plugs/wires, fuel pump, O2 sensors, etc...i havent taken it in to the shop yet or scanned it so im just trying to get some opinions...the car has 37K original miles and is completely stock w auto trans, a fresh tank of 92octane and i added seafoam...it did this before the fresh gas and seafoam too...when you first start it, it runs fine..idles smooth, doesnt shake...once warmed up it will idle rough and have a loss of power and shake once it gets through that she takes off...back into the garage and it smells like rotten eggs really bad...i've had a GM mechanic tell me the O2 senor thinks its running 'lean' and then dumps extra fuel in? if it was the cats wouldnt it do this all the time? thanks ahead of time for any suggestions or opinions!

 

There is a link to a free download of OBD-1 scan software, stickied at the top of the "Computer Diagnostics and Tuning" forum. All you need is a cable, and there is info there on how to build one or buy one. Since it runs fine cold, but exhibits the problem when it warms up, could be a problem with the coolant temp sensor in the water pump, or the O2 sensors. A data log may show the cause. We can look at the data log for you.

 

Thanks Fred!

 

your 02 could be bad....or something causing it to read lean like a exhaust manifold leak causing the pcm to dump fuel

"rotten egg" smell is often associated with clogged CAT. at 37k mi your CATS should not be clogged.

you really need scan software so you can see wtf 02's are doing.

maybe a stuck injector dumping fuel...which if that goes on can clog a CAT. Could be multiple problems but scaning the motor is what needs to happen or you/we are just guessing based on a symptom that have multiple causes.

you could buy a $25 heat gun at harbor freight and read temps front & rear of CAT if significantly higher front side that indicated cloged.

replacing 02 may resolve the problem but if you have a exhaust leak pre-02 than it will read the same. only use AC Delco 02's

 

From what you described it sounds like a clogged cat....

 

with that low of milage the CAT should not be clogged. If it has been running pig rich that can do it. get a heat gun and see if temps are significantly higher front of CAT vs back of it