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2005 Pontiac G6 - runs great till it warms up

For the first five min. it has great power when i put my foot in it it just takes off fast. As soon as it warms up it starts misfiring,backfiring i have to feather gas peddle to keep the power going. If i put my foot in it it just makes it worse. the check engine light is on solid when cold then starts flashing when it warms up. it does show four codes: P0301 #1 cylinder misfire, P0452 fuel tank pressure sensor/EVAP, P0463 fuel level sensor "A"circuit high, P0461 sensor reference voltage A circuit/open.
the car was hit in the front needed fender, hood and radiator. what baffles me is how and why does it run so well cold then so poorly when its warm. no water issues. any one heard of this?

When the Check Light is solid when the engine is cold, it means a major misfire isn’t occurring.

When the Check Engine light starts flashing, it means a major misfire is occurring.

Tester

The other thing is that when an engine is cold, it it running in open loop mode and using pre-set sensor information from the computer. Once it warms up it goes into closed loop and uses the actual readings from the various sensors. Really time to have someone look at it though for a good diagnosis. On mine it only took a few minutes of mis-fire to ruin the $700 cat.