2003 Alero 3.4L Misfire And Burns Gas Like Crazy!!

Mcjewpants

So recently I had a friend of a friend replace the thermostat in my Alero. The cars temp is just fine but since he did it, the car runs extremely rough and became 50x louder than before. Before, you could barely tell the car was running because of how smooth and quiet it was. Like a night and day difference now since he replaced it. From what I can tell, he disconnected the exhaust to reach the thermostat. I believe the flange gasket fell apart and was never replaced before he reconnected the exhaust. My question is would a faulty flange gasket cause so many issues (serious misfire, terrible fuel economy, erratic idle, inconsistent acceleration power, extremely loud compared to previous condition) and also since he had replaced the thermostat, is this a good deduction of what happened?

Mcjewpants

Also, my OBD II codes show an emissions misfire

imidazol97

The leaking of exhaust gas where the gasket used to seal would affect the readings of the oxygen sensor in front of the catalytic converter and after. That is used to adjust the mixture.

I'd be worried about the hot exhaust leaking overheating the surround area and possibly causing a fire.

The problem needs to repaired, correctly. I find it hard to believe the exhaust needs to come off to get to the thermostat, but I'm not there to see the vehicle.

I recommend taking it to a competent repair shop.

thecardoc3

The exhaust cross over pipe runs along the rear of the engine (drivers side of the car) above the transmission and prevents access to the thermostat housing. I don't remember there being any gaskets, iirc the pipe uses flare connections and might be just misaligned.