Why doesn't my car deccelerate when I take my foot off the gas?

Dear Car Talk

Dear Car Talk | Sep 01, 2001

Dear Tom and Ray:

I recently bought a used '98 3.0-liter Ford Taurus with no cruise control. It has about 10,000 miles on it. When driving at speeds above 40 mph, I've noticed that when I take my foot off of the accelerator to allow the car to slow down on its own, it seems to maintain its speed for up to 4/10 of a mile -- and then it finally starts to slow down very gradually. While cars ahead of me are able to slow down by coasting, I find my car rapidly closing in on them, forcing me to constantly brake hard just to keep from running into their back bumpers. Do you have any thoughts as to what might be causing this? -- Frank

TOM: Well, now you know why the previous owner sold it with only 10,000 miles on it, Frank!

RAY: Actually, it's not clear to me that there's anything wrong. I haven't driven a '98 Taurus recently, but some cars are just better "coasters" than others.

TOM: My brother's a particularly good coaster. He coasted through all three of his years in eighth grade.

RAY: Actually, I was thinking of the most recent Buicks we've driven, which were particularly good coasters. That said, 4/10 of a mile is a long way to coast without any sign of slowing down.

TOM: You need to do an experiment, Frank. You probably have a tachometer in your car (if not, ask your dealer to hook up a temporary one for you). The tachometer measures your engine speed. What you want to do is take the car out on a level road and get it up to 40 or 50 mph. Then take your foot off the gas. When your foot comes off the gas, you ought to see an immediate drop in the engine speed. It won't drop all the way down to idle speed, but it should drop down to between 1,000 and 1,500 rpm.

RAY: If it DOES drop, then I'd say nothing is wrong, and your car is just a particularly accomplished coaster. But if the engine speed doesn't drop -- and I suspect that's going to be the case -- then something is causing your throttle to stay open, and that's what's causing you to coast for so long.

TOM: Armed with that information, your dealer should be much better able to help you, Frank. Good luck.

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