I'll do my best to explain this. It's on a 96 5.2.

It's happened once before a few months back. Just got home from a 300 mile drive on the interstate. About 90 miles from home, everytime I let off the gas slowly, the truck would jerk and the rpm's would kind of jump around. When I pressed the pedal again, it would do the same thing until the pedal was pushed down to a certain point where I was just cruising along. Speeding up from this point was fine. It does it with O/D off as well, it's just much more violent because the RPM's are up higher. It's hard to start, and also when starting from a stop, the RPM's will jump down like it's about to die, and I have to give it a good bit of gas to stay on. Now the last time it did this, I disconnected the battery overnight, and the next morning it ran great. Tonight I pulled over at a gas station and disconnected it for about 5 minutes, but it didn't help. Also, the check engine light isn't coming on.

The motor and tranny were rebuilt about 60,000 miles ago. I put in a 180 degree thermostat just for giggles, but it's been running really cold. I'm going to change that out this week back to a 195. Could it be that it's just gummed up from running rich? Any ideas here? Crank or cam position sensor? IAC or EGR valve?

 

Could be the IAC or the TPS.

 

If you live in a cooler climate area, put the stock thermostat back in. Otherwise it will take a lot longer to warm up & not run at the correct temp to make everything happy. As for as your issue, I would first check all electrical connections like both battery cables. After that, do the tests on the IAC & TPS, there should be some stickys on those tests. If that does not do it, I would suspect the EGR. Someone correct me if I am wrong, but the EGR in this truck is still vacuum advanced, right? If it is not the electronic EGR, it could have a heavy carbon build up causing the rod in it to not move, causing issues similar to yours. Cleaning it would work or replacing it, but I vote for doing tests correctly before throwing $$$$ at it that it may not need.

 

I saw the same issue in my shop on one of our trucks. I would def look at the TPS. If you have to replace it make sure you disconnect the batt first.

 

Stock therm is definitely going back in. I'll try those tests. Thanks guys.

 

You could also have some water in your gas tank. Pour in a bottle of HEET water remover just in case.

 

Ok guys...I tested the TPS. The voltage was 0.7 at idle and rose up slowly and steadily to a max of 3.5 volts as the gas pedal was pressed all the way to the floor.

Anything else I should try?

 

Pull some of your plugs, and see what they look like. Did you use a digital, or analog meter to test TPS? (It sure SOUNDS like a tps problem......)

 

I used a digital. It didn't jump down or up. Rose by .1 to .2 volts as it was being pressed. Is a max of 3.5 volts ok? I thought it was supposed to start between .8 and 1.2 then go up to at least 4 volts.

I'll pull a couple of plugs in the morning when I can see.

 

Did you check volts or ohms on TPS? I am assuming volts, with key on? Disconnect battery, remove TPS and read ohms from closed position to fully open. Make sure there are no skips and ohms increase proportional to movement.