Idleing your car

Is it bad to let your car idle? EX: It's cold out so I leave it running for 15 min while I run into a store to keep it warm. Or it's hot out so I keep it running so it will stay cool.

I have heard that it is good because you waste gas at startup. I have a fuel injected engine. Any advice?

Mostly excess idling wastes gas and pollutes the air unnecessarily.
Cars do use more fuel to start up only when the engine is cold. Unless you live in Antarctica, your car will not cool down enough in 15 minutes to create a cold start condition, so switching your car off for a few minutes definitely saves more gas than letting it run.
Cars left idling unattended have a tendency to get stolen, as well.

Ditto the previous post. Especially on modern cars with computerized fuel management. The computer does enrichen the mixture for starting, but typically the fuel system goes "closed loop" within a minute or two (even in cold ambient temps) when the O2 sensors warm up(newer ones, 4 wires, have built in heaters) to operating temperatures. Idleing for anything more than a minute is just wasting fuel.
As far as comfort goes, however, and also warming up the engine oil, etc, warming up a car at idle for a few minutes is a good idea. It was 22°F BELOW here in NH yesterday morning, and I wasted a little fuel to let mine warm up for 15 minutes and it still took another 10 minutes of driving to get the coolant temp up to 195°F.

Yeah, letting the engine warm up does waste more gas than if you were just to drive away...
But, it also lets the oil warm up, and the coolant, and the cats...
And it also warms up the interior of your car (hence the idea of remote starters...).

Yeah, letting the engine warm up does waste more gas than if you were just to drive away...

Talking about wasting fuel at idle, mine surely wastes a lot. I have manualy increased the idle to about 1600 RPM. The reason is that my car "shakes" at low idle and I was wondering if it was unhealthy for the engine.

Is it bad to let your car idle? EX: It's cold out so I leave it running for 15 min while I run into a store to keep it warm. Or it's hot out so I keep it running so it will stay cool.

I have heard that it is good because you waste gas at startup. I have a fuel injected engine. Any advice?

Since you have a EFI car, it hurts nothing to let it idle (other than the waste of fuel). Restarting a EFI engine wastes less fuel than a carbuerated car. Assuming the car is warmed up, I would never let it idle for more than a couple minutes, the restart doesn't take any more fuel than 5 seconds of idling and it isn't going to cool down much in 10-15 minutes.

Jim
SR Racing

Like my friend told me... It's a car, USE it.. If something breaks..FIX IT..

Lol.

Like my friend told me... It's a car, USE it.. If something breaks..FIX IT..

Lol.

Oh so if it breaks, then you fix it. I'm always messing with my truck when it isn't broken.... My truck might run better if I stop messing with it....

I'm always messing with my truck when it isn't broken.... My truck might run better if I stop messing with it....

And so will my car. :biggrin: :biggrin: :biggrin:
But it doesn't matter. I'll mess it up a couple of times, then I'll get it right and stop being an engineering noob.