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Truck wont run- but wont stop either

i have an '89 mitsubishi mighty max. today i got stranded, cause the truck wont go. i push the gas and it sputters. but the strange part is, when i went to turn it off, it sputtered on for 10 seconds more. it will crank and run fine- in idle. any ideas? what should i check for?

The “run-on” can be caused by timing that is advanced too far, a bad EGR valve, carbon deposits in the cylinders, or failure of the fuel delivery system to shut off the fuel flow when the ignition is turned off. Overall, how well has this truck been maintained? All of the problems could be the result of a lack of maintenance, so simply changing spark plugs, air filter, fuel filter, and adjusting the ignition timing could resolve the problems.

the maintenance on this is iffy. my dad bought it from a friend who inherited it for a few hundred. i noticed that the wheels had been changed up from 14s to 15s. on a low hp, low torque truck, this is a bad idea. it doesnt give me much confidence in the former owner. anyway, which of the problems you mentioned could cause it to do this suddenly? it was running fine, and now its not–nothing gradual about it. if it was the plugs, could it idle perfectly? i took the air filter out on the side of the road to see if it was stopping it up, and thats not it. if its only the fuel filter, it doesnt seem that the truck would run on after shut off. ive had many fuel filter troubles in my time. as for the timing, could that have changed suddenly? im not questioning your expertise (lord knows i dont have much) im just trying to get more detail. im so very flat broke–my wife is in trade school and working only part time, im a lowly aide for handicapped people-- so im trying to do a little cheap diagnosis. if you know of ways to check anything that might be wrong cheap or free, please let me know. thanks

I would look for a vacuum leak in the intake system. Look at all the vacuum hoses. Make sure they are firmly attached at each end and not split in between. Clamp off each tube to see if there is a leaking accessory. Finally, listen around the intake manifold gasket, throttle body gasket, etc. for a sound of hissing vacuum. If all else fails, use throttle body cleaner to wet the edges of the gaskets to see if there is a change in the engine idle.

Remember that the hose going to the brake booster is a vacuum hose. Plug it, and the other vacuum hoses, temporarily and see if the truck goes.
Make sure that no electrical connector has become disconnected. It would be a good idea to disconnect, and reconnect all that you see in the engine compartment.
The throttle position sensor (tps) informs the engine computer when you have depressed the gas pedal. It’s next to the throttle body. Make sure its electrical connector is connected.

Do not discount plugged exaust.

oh thank you all so much for your input. my wife is home and i am taking her car up there to check on it. fortunately it acted up less than a mile from the house, next to an abandoned warehouse with a convenient parking lot. i will post back with more when i get back. please continue suggestions in case i come back with more info and need clarification or something

well, i just drove the truck home. i went out there and it revved up fine. came back and got the wife to drive me up there, and she followed me home. it rode fine, but she said she smelled a bit of gas behind me. does this change anything?

There could be a gasoline leak which could cause loss of fuel pressure. Check fuel lines from gas tank to fuel injectors.

anyone know if this is an in-tank fuel pump? how about the fuel filter, know where i can find it?