I have a 2002 SL1 that sporadically idles high - around 1000, instead of 700. As a result, the car "lurches" a bit when first accelerating and braking. When I put the car in "park", it idles at 2000. I doesn't seem to consistently coincide with anything else, perhaps it's worse when the car is first started. It only does this sporadically - some days the car is fine.

I had the same problem this summer and my mechanic diagnosed it as a failed thermometer. It was replaced and the problem went away. Now the problem has returned. Could it be the thermometer again or could it be some other problem causing the same symptoms? Any ideas on what else could be wrong?

I should add that the engine light has never come on and the car has about 86,000 miles.

Thanks!
Sage

 

Here's a quick check for you --> Turn off the car, and disconnect the "thermometer" ... its called the Engine Coolant Temperature Sensor, or ECTS. With an ohmmeter, read the value of the sensor on the block of the engine. If the meter reads totally zero, or theres no reading at all (totally open), replace the sensor again, and this time make sure the replacement part has a brass tip on it

 

Thanks. I'll give it a try.

 

So, I haven't had time to test the ECTS yet, but I did notice another trend. The car only idles high after it has sat in the cold all day while I'm parked at work. While driving home, I tried an experiment - I turned the car off while stopped at a red light and then turned the car back on - problem gone. It seems as though the high idle correlates with a cold car/engine.

 

The problem with a computor controlled engine is that it appears to be very simple in operation. What is difficult to realize is that there is a huge number of things feeding that computor that in turn controls a whole bunch of variables. All of which keep the engine from running crappy.
It could very well be, that the computor thinks the engine is warm when it isn't, thus being controlled incorrectly and it runs crappy. Or
something is broken that lets the engine run well when it is cold but makes no difference when the engine is warm.
The sensor that OceanArcher suggested you check is the one the computor uses to check the temperature of things. If it is sending false information the computor being basically stupid, does not know the difference. And the engine runs crappy.
So
when the engine is cold. Run the test recommended.
That sensor is problem prone and might very well be the problem.

 

Thanks for the info. Haven't had the opportunity to test yet as I'm awaiting an ohmeter. I'll be happy if it is only the ECTS and not something more complicated - but annoyed at the same time since it was just replaced in May.