A high idle speed wreaks havoc on icy roads.

Dear Car Talk

Dear Car Talk | Nov 01, 1993

Dear Tom and Ray:

I have a slick-streets problem with a front-wheel-drive car that my dealer can't help me with. When I am slowing down below ten miles per hour on an icy street, even using the breaks as lightly as I can, the rear wheels lock up, the front wheels keep pulling, and the car goes out of control. On a level, smooth road, the car holds about 35 mph without touching the accelerator. What should I do?

TOM: I'd buy a football helmet, Dave. A set of shoulder pads wouldn't be a bad idea, either.

RAY: Actually, I'd go back to your dealer and ask him to check the car's idle speed. An excessively high idle speed would explain both the inability to stop on icy roads, and the 35 mph "automatic cruise" setting.

TOM: If your dealer says the curb idle speed is OK, have him check the "idle air control." That's a device that increases the idle speed when the engine needs it. For example, when you turn on the air conditioning, that draws power from the engine and makes it slow down. The idle air control speeds the engine back up to prevent it from stalling.

RAY: And when it's icy and snowy out, you're probably using the defroster, which on most cars, automatically turns on the air conditioner. So your idle air control may be over-achieving, and boosting the idle speed too much under those conditions.

TOM: I'd get it fixed as soon as possible, Dave. And until you do, would you mind sending me a map of your route to work so I can avoid those roads when it's slippery out?

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