Engine Mechanical problem
1993 Buick Lesabre 6 cyl Two Wheel Drive Automatic 155000 miles
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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.

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.

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.

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.