87 GMC Pickup Sputtering. Cant Fix

[Viperdude152]

Hey guys

We brought the truck to our mechanic 3 times and he cant find the problem. The whole ignition is new. Plugs, wires, cap, rotor, coil. I guess he put in a newer style of cap and rotor with the coil outside of the cap instead of ontop.

well anyways it sputters like crazy. Well. I shoudl say stumbles..? Basically it feels like from time to time its not running on all 8 cylinders. HUGE power drop and we tow our horse trailer with it. It just happend recently about 4 months ago. The engine will run strong when its cold. But once it warms up it starts stumbling. Almost for the whole day it will run like crap. Now and then it will run great. almost like someone fliped on a switch and then it runs good. Then this switch gets flipped off and the engine runs like crap.

Anyone have this problem before? Its not the fuel pump or fuel filter I have had fuel problems in the past and this deffinatly isnt a fuel problem. Unless im wrong. The truck it throttle body Fuel Injected. Im guessing these have a MAP sensor?

thanks guys. Hope to hear from you!

Justin