Throttle Sometimes Sticks

Tiny
OLDDODGETRUCK
  • MEMBER
  • 2001 DAEWOO NUBIRA
  • 2.0L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
I had an idle problem on my car where the idle would sometimes go really high in park. I ended up replacing the throttle body, which fixed the problem for a few days, then this happened. I was driving home from school, about a twenty minute drive on a highway, and when I tried to stop at a stop sign the car kept pulling, the rpm's would not drop below 2000. I rolled the rest of the signs and made it home, since I had had a problem with a high idle before I anticipated it would rev when I shifted it and sure enough when I put it in park it shot up to around 5000 before I could shut it off. I went to throttle and it was stuck partially open, but the cable was loose. I forced it to close the rest of the way, but I did not have time to mess with it. The next day I went back and the throttle was sticking, so I turned the idle screw about half a turn and the plate did not bind. I test drove it and did not have any problems. Then today I drove it to school without any problems, but on the way back it stuck at 2000 at the same stop sign. I rolled home and sure enough the throttle was sticking again, and when I manually closed it the car idled fine. What would cause this to happen? I cleaned the throttle when I put it on, so it is not carbon build-up, and I just did a smoke vacuum test, which did not turn up anything. Is it possible the TPS is sticking? Any ideas as to why the throttle only sticks in certain situations?
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Monday, October 3rd, 2016 AT 2:13 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
I have never heard of a throttle position sensor causing this, but there is always a first time. For a mechanic, the goal is to get it to stick and stay that way long enough that we can find what is causing it. What I would do the next time this occurs is to stop the engine, then carefully remove the TPS. If the throttle blade snaps closed you found the suspect.

If the throttle blade shaft is sticking, you would have solved that with the new throttle body, but more importantly, the shaft and / or bushing would be ground up making them rough, and that would cause a major vacuum leak that would result in a too-high idle speed all the time, including after you force the throttle blade closed.

What I have run into is with throttle bodies that use a quarter-round cable guide, the cable from the cruise control servo can fall off to one side, then it is not long enough to let the throttle close all the way. There is always an underlying cause for that like a kink in the end of the cable or the mounting bracket is bent or miss-positioned. You would have seen that by now.
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Tuesday, October 4th, 2016 AT 10:51 PM
Tiny
OLDDODGETRUCK
  • MEMBER
I appreciate the answer and I've checked and rechecked everything you have suggested as wells as anything else I can think and nothing seems to effect it. The only solution I have found is to put the idle high so that the plate cant get to the spot where it binds, but that really is more of a band-aid than an actual fix. I have noticed that it only catches when the engine is running, which seems odd to me. I've replaced the throttle body, cleaned the new one until it's shiny, loosened the throttle cable, replaced the IACV, cleaned the TPS, checked for vacuum leaks, adjusted the idle, and nothing seems to help. The plate only catches a fraction of an inch above the normal idle position and if I snap the throttle it doesn't catch. I have noticed a few other things in the past few days; when slowing down the rpms will hit 1000 and bounce back up to around 1300 once or twice before settling down, and the rpms seem to hang if I just tap the gas so that the revs go to 2000 or so. I do sometimes get a high idle code, but no lean or rich codes. I'm thinking since I have 2 throttle plates I could try taking a dremel to one and see if I can keep it from catching. Any ideas, I'm pretty much at a loss at this point.
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Thursday, October 6th, 2016 AT 7:04 PM
Tiny
CARADIODOC
  • EXPERT
I've had carburetors that did this when the throttle shafts got chewed up and became rough. The force of the air blowing against them would cause them to bind, but once they were stuck, they would stay that way after the engine was stopped. The additional clue was sometimes you'd feel them stick, then suddenly pop free when pushing on the accelerator pedal. One got so bad that at times you couldn't even push the pedal. You had to release it, then push it again. Other than the misery of the sticking, those didn't really cause a high idle speed because little air was sneaking in through the shaft and bushings. The fix for those was to just install a good used carburetor. They were so cheap and we all had extras laying around, so it didn't pay to try to fix one. That problem wasn't common either, so it was not likely the next one would do the same thing.

When this happens to a throttle body assembly, the resulting vacuum leak typically leads to a high idle, but I've never run into one that caused sticking. To have two do the same thing really surprises me. I'm still leaning toward the throttle position sensor. Cleaning it isn't going to do anything if there is some mechanical issue inside it. Unbolt it from the throttle body, then see if the sticking still occurs. Those sensors are sealed so you're not going to get any cleaning chemical inside it and onto the sliding contact. I used to take a lot of them apart and connect hidden wires that ran to switches to make "bugged" cars for my students to diagnose. Due to their internal construction, I can see where a mechanical problem could develop, but that would be pretty unusual.
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Friday, October 7th, 2016 AT 12:45 AM
Tiny
OLDDODGETRUCK
  • MEMBER
I replaced the TPS with a different used one, and it made the idle a little smoother, but the throttle still got stuck at 2K. Usually, I turn it off as soon as I put it in park because it revs so high, but today I let it rev with the idle governor keeping it below 4K. I opened the hood and put the plate back to idle, and the revs went back to normal with no binding when I revved it. It felt like something was holding it open, as I felt and heard a little pop, like something was releasing, in the tb when I closed it. There is absolutely no binding at all, besides it catching at 2K, I can't get it to stick by myself, it only happens when I'm driving.
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Saturday, October 8th, 2016 AT 12:49 PM
Tiny
CARADIODOC
  • EXPERT
I'm just about out of answers. The only other thing I can suggest is to look for external linkages or controls that could be causing this. I looked at a photo of your throttle body and throttle position sensor, but from those I can't see any obvious suspects. I also looked at the idle air control valve. That is the same design that Chrysler and GM used for many years. It causes very few problems. Even if that wasn't working properly, you wouldn't see anything snapping free like you described.
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Saturday, October 8th, 2016 AT 1:54 PM

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