I have a 1988 chevy k2500 4x4 350 throttle body f.i. once the motor gets good and warmed up it starts sputtering and back firing and loses all power it only does this in gear not in neutral or park?

You didn't say what engine ect. but I would look at the stepper motor mounted on the throttle body or the Idle Air Control in the throttle body. Use throttle body/intake cleaner not brakekleen or carb cleaner.

Suggest you have injector balance test done , leaking fuel injectors , maybe .

Try cleaning the throttle body and the idle speed control valve, they get full of sludge and this causes stalling. Use a product called CRC Throttle valve cleaner on both parts, DO NOT USE CARB CLEANER IT WILL RUIN THE PARTS.

Hello, just had this problem myself. Check your EGR valve by pulling the vacume line off and pushing up under the valve put your finger over the vacume line hole and release the valve, if it returns to normal position then its bad if not its good. If its bad it needs replaced. Mine did the exact same thing and thats what it was. Hope this helps

Recheck your firing order for basics. If this is in good, a compression test may be necessary. Which enigine do you have?

EATHER IS NOT GOOD , ITS FOR COLD COLD MOTORS.. CHECK YOUR FUEL PRESSURE AND GAS FILTER .YOU MIGHT HAVE A BAD FUEL PUMP ITS IN THE GAS TANK!!! . USE CARB & CHOKE CLEANER ..PARTS MASTER # 1736 ..ITS NOT AS HOT AND WONT POP A HEAD GASKET .IF'N I WAS ANY HELP AT ALL PLEASE VOTE.. JAY

ICM idle control module, loc throttle body, it may be dirty, remove clean or replace, its easy..

You could have a dirty EGR valve, you can re move it from the manifold and clean it with Throttle body cleaner. Might as well buy two cans, since your cleaning the EGR, might as well clean out the throttle body too.
Spray the throttle body cleaner in to the throttle body with the engine running and try to keep it at 1000 rpm and then to 1500 rpm as you clean out the throttle body and let it idle down for 2 min then turn the engine off. Then turn the engine to the run position for 10 seconds and start and let idle, ro for a test drive and hope that solved the problem, if not there a few more things we can do which will consist for tune up.
Note: Clean the EGR first so you don't burn your self since the engine would still be cool before you clean the Throttle body.
Good luck and keep me posted.

Chk. your egr valve, that it is not sticking and you got vacume to it. could be carboned up and is not working.

Check your intake and exhaust modules. I have a 1987 D21 and had the same problem (if I understand your post). I replaced the modules located behind the driver side headlights and it fixed the problem. Good luck! I hope this helps.