1993 Buick Lesabre Please Help! Replaced TPS 4 times.

RBRIANRAMEY

MEMBER
1993 BUICK LESABRE
6 CYL
2WD
AUTOMATIC
155,000 MILES

I bought this car with a statement that it needs a new throttle position sensor per the previous owner's mechanic. The car was idling extremely high. It would accelerate and hold a speed of about 45 mph without touching the gas. I had the TPS replaced and it was fixed for about a month. The car began idling very high again sporadically. Sometimes it would idle normally after sitting at a stoplight for a little while. Other times turning the engine off and restarting would temporarily fix it. The engine light did not initially come on, so my mechanic could not get a trouble code. We replaced the idle air control valve with no improvment. We found that by forcibly pushing or twisting the plug/tps the idle would change. We replaced the tps and the plug. The car ran fine for a few weeks. The problem again recurred with the same progression as before until it would idle high all the time. The engine light came on after a few more weeks. This time I took it back to my home town to a trusted mechanic. He stated the tps was at fault, and a coolant leak was causing the sensor to go bad. He took off and cleaned the throttle body, replaced all gaskets/seals, the tps, and the plug. It ran fine for almost two months and again started behaving the same way. The is no coolant leak. I took it back to the home town mechanic. He showed me the tps code, and showed how tapping the accelerator changed the tps setting from less than 1% to over 1%. He said he could not fix it. I had a local mechanic replace it again. It has only been two days and is idling high again. All these parts have come from Autozone and are made by Wells. It has been swapped under warranty 3 times, but I am still paying labor. This problem has got to be rough on my engine, brakes, and gas mileage. Please help! Oh, we also sprayed stuff around the intake looking for leaks and both mechanics say they can't find a vacuum leak.

5 Replies

JALOPYPAPA

MEMBER
467 POSTS

Sorry, I don't know the answer, but I'm puzzled why the "trusted hometown mechanic" would say it was damaged by coolant and then say he couldn't fix it when it went bad again. Did he decide he was wrong about the coolant? Or is he sure coolant isn't leaking again? It seems to me possible there could be a coolant leak internally in the throttle body that you couldn't see without removing it, and it seems at least theoretically possible such a leak could damage a potentiometer. I've always thought it odd the throttle body gasket is paper, although there's a water passage through it into the manifold. When I replaced mine, I applied sealant around that part of it. Maybe he did, too.

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Wednesday, July 2nd, 2008 AT 12:07 PM

RBRIANRAMEY

MEMBER
2 POSTS

Thank you very much for your reply.

The mechanic said there was a leak from the throttle body which he fixed. He also said his diagnostics pointed to a bad tps which he replaced. The car ran fine for about 2 months. On taking it back to him, he again showed a bad tps. Since I have had so much trouble with it, and he has done what he thought would fix it, he thinks something else is going on and offered to refer me to another mechanic he knows that may have better luck.
The tps is mounted externally on the bottom of the throttle body, so I would be able to see any coolant leaking onto it. When I just had it replaced again here by a shade tree mechanic it is likely coolant got on it again, but the thing is mounted 2 inches away from the coolant bleed valve! I don't see how a few drops of a liquid contacting a component exposed in the engine compartment is going to make it go bad. The little peice of paper included with the part states that coolant contacting the pcb would make it malfunction. But it seems a part in the engine compartment should be sealed from moisture and fluids.
I think I may have to take it to the mechanic I'm refered to, but he'll cost a couple of hundred, and that puts the total cost so far at about $800.00. I only spent $1000 on the car.
If you have any other suggestions or know of this being common, please let me know.

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Wednesday, July 2nd, 2008 AT 12:29 PM

JALOPYPAPA

MEMBER
467 POSTS

Thanks for the explanation. I was wondering if maybe the coolant is leaking INTO the TPS as opposed to ONTO it, in a way you can't see from the outside. Maybe there's a tiny crack in the throttle body's water passage, just enough to allow water to seep into the tps housing.

Just a wild guess. Anyway, at this point, maybe I'd consider replacing the whole throttle body. Looks like a new one is $345, though. You could get a used one I guess for half that.

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Wednesday, July 2nd, 2008 AT 1:16 PM

DBA DEAN

MEMBER
1 POST

I recently purchased a pristine 1993 Buick LaSabre with 28,553 miles. Worked great for 2 weeks then hard to start for a couple of days then no start. Took it to mechanic who didn't have a OBD1 scanner. So I told him how to get trouble codes with a paper clip, the trouble code then was the TPS, he gave a quote but suggested it could be more expensive and could not promise this would resolve the issue. I asked him if he had checked to make sure that the 3 wires that connect to the tps were doing their job correctly, he replied that they had not looked at that and would have his electrical guy to check .. Here is a link to a great video that explained a great deal as to what can give you a trouble code to the TPS and what other factors can cause these problems. https://www.youtube.com/watch?v=FJobCD6y8fk

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Tuesday, August 8th, 2017 AT 9:46 AM

CARADIODOC

MECHANIC
33,871 POSTS

This post is nine years old, but thank you for the addition. The biggest misconception that you eluded to is the fault codes did not say to replace the TPS or that it was bad. Fault codes never say to replace a part. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition.

Water gets in the engine compartment any time it's raining, and water will not hurt a throttle position sensor. The other misconception was that the fault codes couldn't be read because the Check Engine light wasn't on. On '96 and newer vehicles there can be over 2,000 potential fault codes. About half of them refer to things that could adversely affect emissions. Those are the codes that turn on the Check Engine light. If any of the other 1,000 or so codes are set, the light never turns on, but they can still be read. '95 and older cars only have a few dozen potential fault codes, but still the Check Engine light only turns on for those codes related to things that could affect emissions.

The biggest clue that was glossed over was wiggling the connector had an affect on the symptoms. The way to approach this is to view the TPS signal voltage on a scanner while moving the connector. It is fed with 5.0 volts. Due to mechanical stops inside it, the range of signal voltage goes from 0.5 volts at idle, (approximately), to 4.5 volts at wide-open-throttle. If the signal voltage is wrong, but stays within that range, no fault code will be set. A broken ground wire will send the signal voltage to 5.0 volts. A broken 5.0 volt feed wire will send the signal voltage to 0.0 volts. Either of those conditions will trigger a fault code for "TPS voltage high" or "TPS voltage low". It is possible, but very rare, to have one of those breaks occur inside the sensor itself. The chance of that happening to a second or third sensor is very unlikely.

My suggestion was going to be to replace the plug, but that was done already. That leaves just one last suspect. The 5.0 volt feed wire and the ground wire for the TPS are shared with a number of other sensors. Only the signal wires are specific to each sensor. That means those two wires each have a splice in the wiring harness. Those are just ripe for corrosion and intermittent problems. My suspicion is it wasn't changing parts that made the engine run better for weeks or months. It was flexing the harness while doing the repairs that caused the change in symptoms.