I have a 2001 impala with the 3.8. I've recently been experiencing a problem I can't figure out and after researching on the Internet, troubleshooting with a Haynes manual and asking multiple mechanics their opinion I am clueless. I've tried jus about everything short of replacing the PCM. The problem is I go out and start it and everything works jus fine. After about 20 seconds it starts surging really bad for about 30 seconds. Then it runs fine again for about 30 seconds and then it dies. If I try to start it after that I have to keep my foot on the gas to keep it running. So far I put new spark plugs, spark plug wires, fuel filter, fuel pressure regulator, MAP sensor, MAF sensor, IAC valve, PCV valve, throttle position sensor, I checked the fuel pressure, tested the fuel injectors, replaced the coolant temp sensor, hollowed out the catalytic converter, checked for vacuum leaks, checked all the fuses, checked all my grounds, tested the fuel pump, ran some seafoam through it. I have no clue what else it could be. Any thoughts?