When cold, engine starts and runs perfectly

When cold, engine starts and runs perfectly. When the engine temp gauge gets about to about 1/4 of the scale, engine will stall and won't re-start. Backfire thru exhaust. Ocassionally will start but runs VERY rough, when placed under load, immediately stalls. Let engine cool down, starts and runs fine.

This problem started as and occasional "bump" while driving. Then got to where it would run badly for about 10-15 seconds. When it does runs, it runs smooth and clean.

Drive symptoms are like you are running out of gas. Items I have replaced with that have not fixed the problem - Fuel filter, Fuel Pump Relay, Fuel pump, and Fuel Pressure Regulator. I also checked the C305 connector (under carpet behind drivers seat) for corrosion or loose connections but all were clean and tight.

Since this started, the PCM has not recorded any errors. As a test, I have disconnected the ERG valve plug and the no error codes. I then pulled a couple of other sensor plugs and still no error codes. It is like the PCM will no longer register error codes.

I am at a loss. Any ideas?