Car runs fine until warmed up then spits and sputters and misfires. I have replaced , knock sensor , fuel filter, air filter , dist cap rotor but, plug, wires, air filter , done oil change. had put on a machine and have fire and good compression in all four cylinders.????

Best guess is O2 sensor is reading too much unburned fue in the exhaust for some reason and leaning out the fuel flow to compensate. Runs when you throw more throttle at it but leans out as you try to hold steady speed. Should throw a code though.

TUNE-UP, SPARK PLUGS, WIRES, AIR & FUEL FILTERS, FUEL INJECTOR CLEANER IN TANK, ALSO REPLACE PCV VALVE, & MOST IMPORTANT, REPLACE EGR VALVE, IT GETS TOTALLY CLOGED UP, YOUR ENGINE IS KNOWN FOR THAT. I HAVE A GNC 2500, 3/4 TON. SEEN IT ALL. CHANGE YOUR DISTRIBUTOR CAP & ROTOR ALSO. JUST DO IT !!!!!!!!!!!

CLOGGED FUEL FILTER OR CLOGGED FUEL INJECTORS.WILL CAUSE SPUTTERING AND MISFIRE.LEAKING EGR VALVE WILL CAUSE ROUGH IDLING SPUTTERING.

how are the tune-up components,if they need replacing this can happen as the extra fuel when cold puts more stress on weak components.(plugs,wires,cap,rotor,air filter,etc)it could also be carbon build up on the back of the intake valves,this can cause the carbon to absorb fuel(like a sponge)until either the car warms up or the carbon is saturated.this can cause a lean condition when cold.the way to correct this is to have a top end fuel service were a chemical is run through the motor to break up the carbon and clean the intake surfaces.

5 years ago for cap & rotor???? It sounds like it's in dire need of a complete tune up - plugs. wires, cap, rotor, all fluids & filters ESPECIALLY fuel filter. I'd start there and run a good fuel system cleaner through it. Do your tune ups more frequently like every 30K - not wait 5 years!

I had the same problem, till i found out that the box where my air filter is was cracked underneath. its the secondary box just after the sensor for the air filter. It was sucking in too much air. I removed it and capped off the hole. check for any cracks past the sensor. once i did that, it straightened right up.

How about the pick up coil in the distributor? A trick we used to use back in the day was to tap the distributor housing with a hammer, key word tap. If the engine missed or stalled than the pick-up coil was replaced.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

sounds like dirty fuel filter or failing fuel pump.

Hi JHWalker
I would try doing the fuel pump filter or fuel pump itself if they are one unit.

Hope this help you.

Matt

Replace the fuel filter.