i just got a used 2.0lsj put into my cobalt cause i blew my last one. i have an aem wideband air/fuel guage installed. and when i use heavy throttle and slowly let off the gas, my engine light flashes, and my air/fuel guage shows im running rich. and the code from the engine light is saying theres a misfire. put a tap the gas pedal briefly than it goes back to normal. whats going on???

 

When you get on the gas, the PCM goes into Power Enrichment Mode.
This makes the engine go Rich. This is normal, as the excess fuel will
act as coolant to help prevent overtemping your engine. As the excess
fuel absorbs heat, it will aslo expand giveing you some extra power,
but will not combust due to lack of oxygen.

Your CEL / MIL flashing, indicats misfires.
If your misfireing when you really step
on it, you might be getting "Spark Blow OuT"
Check your plugs and check the gap.