Truck tries to drive through the brakes

[PJones96]

I wonder, while it had that high idle, if you had gone out and manually closed throttle if it would’ve gone back to 0° throttle angle and stayed. Just to see if it was sticking mechanically.

I did not, but I did rev the engine multiple times with the accelerator thinking if I opened the throttle blades maybe they would "reseat" and close completely. The engine always went back to the 1040 idle and TP% like I said before. It never resolved.

Should I try a new TPS or am I back to looking at the throttle body itself?

 

[Schurkey]

I'd be looking for TBI loose on the intake manfold, throttle shaft looseness in the TBI casting, and TPS looseness on the throttle body (loose screw(s)).

Finding nothing, I'd look for damaged wire harness allowing the wires to pick up RFI that's screwing with the signal.

I wouldn't even consider ECM until I'm absolutely certain of the rest.

 

[Caman96]

If it is the throttle body, and you have some stupid money lying around…

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[Stockdale Dave]

I had to move the truck yesterday out of the way. This is a cold start scenario. Truck started like normal, put it in drive and it stayed at a normal idle for a change. I drove about 50 feet and put it in park. Once in park the tach jumped to 1500 rpm. It would not "idle down". I plugged up the scanner and looked at the live data. The TP% kept moving between .4 to
.8 to 1.6%. I did not have my foot on the accelerator. The scan tool said the truck was idling at 1040 rpm.

The TPS was replaced within the last year. It was one of the first parts I threw at the problem. Can a parts store like Orielly or Advance test a PCM?

I worked at Oreilly for over 3 years. We could not test TPS units. If it was bought there it could be swapped for a warranty exchange depending on product line. Masterpro had a one year warranty. Standard or Borg Warner had life time. I doubt the TPS is your issue.

 

[PJones96]

I wonder, while it had that high idle, if you had gone out and manually closed throttle if it would’ve gone back to 0° throttle angle and stayed. Just to see if it was sticking mechanically.

It happened again today pulling in the driveway. I was not able to rotate the throttle blade closed at all. It wasn't stuck open is what I'm trying to say. I think if it's related to the TB then it's got to be where the TPS is. I'm going to remove the TPS and check that out one more time. If I can't resolve it that way I will purchase the gold plated TB that you linked to.

 

[Caman96]

It happened again today pulling in the driveway. I was not able to rotate the throttle blade closed at all. It wasn't stuck open is what I'm trying to say. I think if it's related to the TB then it's got to be where the TPS is. I'm going to remove the TPS and check that out one more time. If I can't resolve it that way I will purchase the gold plated TB that you linked to.

Well, I’d only purchase that if it was confirmed your TB was no good. It might also be worth looking at a used TB, but that’s up to the individual.

 

[PJones96]

I've looked at the new and used TBs for sale online. The used ones can be returned but the new one can't. My plan, at the moment, is to buy a used one and see if it changes how the truck runs at all. If it does, great. If the used TB doesn't change anything I can return it. It will eliminate the TB being the issue by not fixing it, or it will fix the problem and prove that the TB was worn out.

I know I'm getting 5 volts to the sensor and I know that when the key is on but not running that the TPS reads correctly 0.0%. I'm thinking there's some play in the shaft of the TB so when the truck is running it's throwing off the TPS from the vibration.

 

[PJones96]

Bought a used TB from a used parts seller online. The truck it came off of had 130k miles on it. That's about half of what mine is at right now so that's pretty much new in my book. It had a IACV and TPS on it out of the box. I took them off and cleaned the whole thing, all the nooks and crannies. I put the IACV off my truck's TB on the "new" TB but put the "new" one's TPS back on it after cleaning it because why not.

It was dark by the time I got the new TB on the truck. I cranked the truck and it acted exactly the same as before. The idle blips intermittently at random when cold. I didn't let it run that long because I was frustrated and went inside and poured a glass of bourbon.

This morning I hooked the scan tool to the truck and could see that powered on without the engine running TPS was reading 0 and seemed to have no dead spots or issues as I played with the pedal. When I started the engine the TPS would go from 0.0 to 0.4 to 0.8 sometimes, almost constantly changing. I drove a 5 mile loop around my house with a couple traffic lights.

It tried to drive through the brakes at the first stop light with the TPS reading 0.4. I held it with the brakes for a second or two and then it idled down to normal. The TPS read the same the whole time.

At the next traffic light I stopped at the TPS read 0.4 but the truck slowed down and idled down like you would expect. No issues at this traffic light even though the TPS read the same as when it wouldn't idle down. I stopped at two other intersections without having an issue.

I pulled into the driveway, put the truck in park and it revved up to about 1500 for a second and came back down to normal pretty quickly.

I do think that the new TB is better than what I had. I'm trying to not psyche myself out just because I put a new part on the truck, but throttle response seemed better and it idles smoother. I think I have a multi-faceted problem here and the throttle body was just one part of the issue.

 

[Erik the Awful]

When I started the engine the TPS would go from 0.0 to 0.4 to 0.8 sometimes, almost constantly changing.

That's an issue. You should have 0.0-0.3 with your foot off the throttle and it should smoothly progress up to 4.0v (+/- 0.5v) as you step into the throttle, return smoothly as you lift, and return to the low value.

 

[John Moore]

Any updates?

I have a very similar issue. Driving me insane.