warm misfire

[z28]

Lets see if anyone else has had this problem. My truck has a misfire when warm on the second start. If i go out and start it in the morning it runs fine. I can drive where im going with no issue. Once i shut it off then restart it, it has a horrible misfire and lack of power. It had a P0300 random misfire code for cylinder 3. Some times the SES light blinks when the engine is under load. I replaced cap rotor and plug wires as they showed some wear. I checked the plugs they all look fine and are not that old. This did not help. I cleaned the MAF, throttle body and IAC. I even tried a different MAF. I tried unplugging one 02 at a time and noticed no change. I also ran it with no cat, still no change. Any ideas would be appreciated. Im not sure where to go from here and i dont want to throw a bunch of unnecessary money and parts at this thing.

[killian96ss]

Could be the fuel injection spider assembly under the intake manifold. There is an upgrade from CPI to MPI. I had a similar problem on my old 01 CC and when the spider assembly was upgraded by GM it ran much better and gained a little better gas mileage.

Steve

[ApproachMedium]

If it only does it once warm, try unplugging your upstream O2 sensors when cold and then start the truck. I had the exact same problem with my v8 swap the driver side of the engine would not fire basically because the sensor was seeing it too rich, and leaning it out to the point of no fire on the drivers side. Unplugging the sensor forced the computer into a "default" mode and it worked fine. I drove it that way for 2 months including all the way to Ohio and back!