Dear Car Talk:
Today, as I released the clutch, I noticed that my car would start driving away like normal, even though my foot was never on the gas pedal. Instead of stalling out, as it normally would do if I didn’t give it gas, it just started moving, as if it had an automatic transmission. Any idea what’s going on? It’s a 2009 Subaru Outback. — Kelly
Hang on while I ask NORAD if there’s been any paranormal activity in your area, Kelly.
Actually, I’m not sure anything is wrong. If you’re good with a clutch, you can get most manual-transmission cars moving in gear without using the gas pedal. And most cars will go 10 mph or so without you stepping on the gas at all.
But it sounds like you’re saying something has changed; I’m guessing it’s the idle speed. If you look at the tachometer, you may see the needle pointing to 1,300, 1,500 or 2,000 rpm instead of where it usually sits, probably a little below 1,000.
Why does that happen? It could be nothing more than the outside temperature. The computer will automatically raise the idle speed when you first start the car in cold weather, to keep it from stalling. Under normal conditions, the idle speed will automatically drop back to normal once the car is warmed up — usually a few minutes, at most.
But if it’s staying elevated (or if you live in Havana), there could be a mechanical problem that’s caused your car to idle high. For instance, you could have carbon buildup on your throttle plate, which is keeping the throttle stuck open a little bit. Or, since you have an electronically controlled throttle on this car, you could have a bad sensor that’s feeding faulty information to the computer, which is then raising the idle. That’ll eventually make your Check Engine light come on — if it’s not already on by the time you read this, Kelly.
So check your tachometer when you start the car tomorrow, and see what it reads. Then check again five minutes later. If it starts a little bit high and comes back to normal, then it’s probably related to cold weather, and you can ignore it. But if it starts very high (say, over 1,500 rpm), or stays high after a few minutes of driving, then it’s time to have someone take a look and figure out what’s causing that. Hey, at least you won’t stall in the meantime, Kelly.
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