Car Talk

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

DEAR KELLY: Hang on while I ask NORAD if there has been any paranormal activity in your area.

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 has 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 sending 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.

DEAR CAR TALK: I really enjoy reading your column. You recently answered a question about synthetic oil, and you recommended using it. I've used synthetic oil for years, with great results. What about using oil additives? They claim to reduce friction and extend engine life. I have used Slick 50 for years, and have now started to use a German product, Moly Lube. Do you recommend products like these?

-- Tom

DEAR TOM: Moly Lube is an engine additive? I always thought it was one of those "adult products." My wife's going to be really upset when I break the news to her.

Do I recommend oil additives? No. I think they're all unnecessary.

The grade of motor oil recommended by your manufacturer, in general, has all the friction-reduction properties you need. And full-synthetic motor oils are even better and, more importantly, hold up better and last longer.

I don't know anything about Moly Lube's claims. I do know that Slick 50 paid $10 million to settle Federal Trade Commission charges of false and unsubstantiated advertising some years ago. I also know, in general, that over the years, many people have gotten rich selling unnecessary potions, additives and elixirs to the gullible auto-owning public. My wife reminds me of that every time I splash some MiracleGro on my ever-widening scalp.

Seriously, the proper oil for your engine (and I do like synthetic), changed regularly, is all your car needs to reduce friction and delay wear and tear.

If you want to do more to help prolong the life of your engine, I think the most effective thing you can do is change the oil a little more often than is recommended. So if the synthetic oil calls for a change every 10,000 miles, change it every 7,500 or 8,000 miles.

And just as importantly, drive gently. Jackrabbit starts and hard acceleration do more to shorten the life of an engine than just about anything -- short of lending the car to your teenage progeny. Good luck.

Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting

cartalk.com

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