[LoneRonin]

I have a 2002 Celica GT, recently it began idling rough had laggy throttle response and was misfiring. I scanned the CEL and got these codes; p0300 p0303 p0302 p0304 p0171 p0420. First thing I did was replace the o2 senors. This made the car run even worse. I checked my coils and spark plugs both were pretty bad so I replaced them, now the car doesn't run. It will start, idle rough and then stall out. If I turn the key all the way to the "off" position and try again it does the same thing, but if I leave the key in the "on" position and try to start it again it will not turn over. A mechanic tried spraying carb cleaner in through the intake manifold when we started it and that kept it running as long as we kept feeding it the carb cleaner. My first thought was a fuel problem so I checked the pump and it is good. Now Im running out of ideas and need help. Any ideas would be greatly appreciated.

 

[LoneRonin]

Alright so I'm going to check out the fuel filter and injectors today.
I cleaned the MAF that was actually the very first thing i did.
Checked for vacuum leaks when it was still running and didn't find any.
I did not reset the ECU after I replaced the o2 sensors. I have a scanner so I'll resetting today.

Thanks for the suggestions.

 

[LoneRonin]

I assumed the misfires were cause by the engine running lean, not to mention my plugs and ignition coils were pretty bad.
Am I wrong in thinking that bad o2 sensors could cause the engine to run lean?
Also,since my car won't run, is there anyway I can test my catalytic converter without it running?