My 2004 Impala starts and runs fine for about 2 minutes, then runs very rough and dies if I don't keep pumping the accelerator. There are NO engine codes. I have replaced the plugs, wires, coils, ignition module, fuel injectors, mass airflow sensor, coolant temp sensor, and the upper and lower intake manifold gaskets. Before I did all those things, I had 4 different engine codes, but now have none after doing all the work. I have also replaced the fuel filter, and the fuel pump was replaced last fall. I am at a loss for a solution now. Need help, please!

 

unplug the pre cat 02 sensors and see if that makes an improvement. the car will run in open loop, ignoring the 02 sensor data until the exhaust becomes hot enough for the 02 to generate a signal. Maybe the 2minutes of proper running is open loop and then it goes into closed loop and runs bad.
Use your scan tool to monitor 02 sensor data. the sensor should show 450mvolt bias voltage until the sensor goes into closed loop.

-view the fuel trim when it goes into closed loop...it should be 0% +/- 10% if its more or less than 10% you have a fuel trim problem.

 

Thank you. I will give that a try. Appreciate any help at this point. As I get older, my patience gets shorter....

 

Just wondering if you found the problem yet?
In the past with several GM 3.8's, I have had the same problem, and each time for me it was a "dirty" MAF sensor. In some cases careful cleaning fixed it, and in other cases I had to replace it. If you try to clean it, I'd suggest get on the internet, and read a lot about it, because that sensor is rather delicate, and can be easily damaged. -and not just any type of cleaner will work,,,
-and just like you, no codes to help.