Ok, so my dad recently picked up this truck with a rebuilt motor in it, after about a week we got the thing running. He drove it around for another week or so and noticed once the engine warmed up the idle would begin to lope. We asked the dealer and ended up replacing the TPS. Once we got it back together we cranked it back up and the engine ran fine at idle. NOW, when its being driven around town, it starts loping when you press on the brakes. But it will not begin loping straight from idle, you have to accelerate first. Anyone have any suggestions? We're back in checking the TPS thinking maybe we got a bad one.

 

what's the engine idle rpm?

 

it goes between 800-1500rpm

 

Okay.
First get the idle speed set correctly with the engine warmed up. What the engine does when cold is NOT important at this point in time- that's a different system which depends on warm idle being set properly. So, engine warmed up, idle at 750 rpms, timing at 5 BTDC.
After that's done, we'll figure out the rest.... And I'm guessing you're going to be having problems getting the idle speed and timing set. We'll be here to help.