Dear Tom and Ray:

A friend of mine has a 1997 Honda CR-V, which he bought used a few years ago. It is generally in good shape but has a problem that has become more and more alarming during the past year or so. Sometimes, while driving, the engine will start to race, and the car refuses to slow down. When the engine is racing, my friend has to step on the brakes very hard to get the car to slow down. Usually, after getting the car to slow down, the engine stops racing. But lately, sometimes it hasn't stopped racing. It seems to be getting worse. The CR-V has been to the dealer several times, but the mechanics have found nothing. The problem doesn't happen when they have it. They say they have never heard of the problem. What could this problem be? Is it fixable? Thank you for your help! -- Neil

RAY: Funny you should mention it, Neil. Just the other day, we had a 1997 Honda CR-V in our shop with the same exact problem.

TOM: So, what was it?

RAY: We had no idea either. We couldn't get it to misbehave for us. We checked the computer for codes, to see if any of the engine sensors were malfunctioning. We found nothing. We checked the database for any service bulletins or anything that would provide a hint. Nada. So finally, out of desperation, we cleaned the throttle body and added some fuel-injector cleaner to the gas tank.

TOM: And that fixed it?

RAY: Well, no. Not really. We still don't know what's wrong with it. But I'll tell you what I plan to do next, when the customer comes back in waving a baseball bat at me. I'll try to clean the idle air control.

TOM: The IAC is a device that's responsible for boosting the idle speed when certain conditions are met. For instance, if the fuel-air mixture is too rich, a sensor will send a signal to the car's computer, and the computer will instruct the IAC to send in more air to boost the idle.

RAY: Or, if you turn on your air conditioner, which requires a lot of power, a sensor tells the computer that the air-conditioning compressor is on, and the computer then tells the IAC to raise the idle speed to compensate for the extra load. So it's possible that the IAC is sticking in the open position sometimes. And perhaps cleaning it will solve the problem.

TOM: You think so?

RAY: Well, no. Not really. Actually, it might. But if it doesn't, I'd probably replace the IAC next, which is roughly a $400 job.

TOM: OK. Now I know why you want to try cleaning it first.

RAY: Right. Unfortunately, if it's not the IAC, you'd have to look next at the computer itself. But in all my years of working on CR-Vs, I've never had to replace a computer. So I doubt that's the problem.

TOM: We'll certainly report back if we solve this problem, Neil, and you guys do the same (or, if anyone else has solved this problem on a CR-V, drop us a note at our Web site, cartalk.com).

RAY: But in the meantime, at least make sure your friend knows that he can always shift into neutral when the engine is racing. That'll stop the car from accelerating, and it's far preferable to crashing.