My 2000 Protege LX has 68,500 miles, low mileage for its years because I ususally just do street driving. Recently, I was driving on the freeway and I lifted my foot off the accelerator. Instead of slowing down, my car kept accelerating on its own to 80 before I hit the brakes and brought it down to 55 mph. I lifted my foot off the brake and the car kept accelerating. It was at 75 when I started braking again. Fortunately, there was no traffic on the freeway. I was able to exit to a relatively abandoned street, where I brought my car under control by braking and bringing the speed down to 40 mph before putting it intoneutral. At neutral, the tachometer showed the engine revving at 4,000 mph in neutral.

I have had a previous check engine light code for an oxy sensor problem, so when I brought it to a mechanic, an oxy sensor code came up and no other. He claimed up and down that an oxy sensor problem could not have caused the problem described. He gave up on diagnosing the car after holding it for two days and turning off the computer code. When he first got the car, the car revved like crazy in park and shot out like mad in drive. After about three minutes of driving, the car suddenly stopped accelerating like crazy, but it continued to idle high. The mechanic said he drove and drove and drove for those two days so he could get another code and replicate the problem, but it didn't come up.

I brought it to another mechanic, a family friend. While driving the car, I noticed that it "sailed" after I lifted my foot off the accelerator, meaning if I lifted the foot off the pedal, it stayed at 40 mph for three seconds before slowing down. Additionally, the tachometer showed the car revving at the same high rpm for those three seconds before coming down.

This other mechanic held the car for two days, trying to replicate the problem, as well. But, he couldn't come up with a conclusive analysis because nothing came up on the computer. He guessed idle air control valve, but said he was only 80 percent certain that was what was causing the problem.

After a $500 repair bill and a new IAC valve, we got the car back and it seems OK, but I am very concerned. I am not sure that the problem is completely fixed. The check engine came up yesterday after I filled the gas tank and added feul injection cleaner. Then it came off this morning. The car idles at 1,000 rpm in park. I don't know if that's normal. I don't know what else could have caused this problem of uncontrolled acceleration and high idle.

Any thoughts? Any advice? Because of my primarily street-driving pattern, we're thinking of trading and getting a hybrid, but we'd rather not have the car payment.

 

After hearing your description, I too would have gone for the IAC valve first. Being that it is the most likely suspect. A Mass air flow sensor would be next, but usually that does the opposite. I hope everyone check for a sticky throttle cable.

Stay as far away from Hybrids as you can. You don't actually get much better mileage than a standard civic or corolla. Also, anyone that knows how nickel is mined, (the primary ingredient of the batteries), knows it is one of the most environment destroying processes in the world. Plus, the cost of ownership of all hybrids is actually higher over a five year period.

 

And when you have to replace the electric battery, they hit you for 8K or so more. But a Civic/Corolla/3.