To idle or not to idle -- it all depends

Dear Car Talk:

When my sister and I shop, we save time by having lunch in the car. When she drives, if it is winter or summer, she will leave the car running for the half hour we eat, so she can run the heat or air conditioning. When I drive, I think that practice is not good for the car, so we suffer with the motor off.

Is it acceptable to idle the car so we are comfortable? Thank you. -- Annette

RAY: Idling doesn’t harm the car at all, Annette. If your sister starts idling near the mall, that’s another issue. But idling is no problem for your engine.

As long as your cooling system is working (and you’d know if it wasn’t because you’d see a “HOT” warning light on the dashboard), cars can idle indefinitely. Or until they run out of gas.

Idling is actually easier on the car than driving. The engine is doing very little work. I guess that’s why they call it idling.

But there are two concerns, and they’re related. One is pollution. When you sit there idling, the engine is still putting out carbon monoxide, carbon dioxide, unburned hydrocarbons and nitrous oxide compounds.

And because of that pollution, the second concern is that many towns and cities now have anti-idling ordinances. Those limit the amount of time you can legally let a vehicle idle without shutting it off. So check your local regulations.

That said, if your teeth are chattering, or sweat is dripping off your chin onto your fish tacos, there’s no reason to suffer. You don’t want to be wasteful, but you also don’t want to end up with frost bite or heat stroke.

So the real question is: Is there room for compromise, especially when the weather is more moderate?

If it’s, say, 80 degrees out, you can idle the car and run the AC for five minutes and then shut it off until you feel uncomfortably warm again. Or you can open the windows from the outset and run the blower fan without the AC in the car’s battery mode.

And if it’s 50 degrees out, you can run the engine and the heater until you’re toasty and then shut it off until you need some more heat. And on days when the weather is more extreme -- here’s an idea -- you can go into a restaurant, live it up, and use the bathroom, too.

Be careful not to dismiss knocking as ‘bad gas’

Dear Car Talk:

I love your column, and thanks for helping us all out with the poltergeists in our cars!

I have a 2018 Chevy 2500HD Silverado with a 6.0 V8 and the trailering package. I pull a 6,000-pound trailer with it.

After I get gas, hitch up my trailer, and hit the open road, within about 30-40 miles, the poltergeist in my truck turns on the “check engine” light.

Since I have OnStar, I have them run a diagnostic, and it’s always the same code: “P0324 ECM Engine System.” This has happened three times. After I unhitch the trailer and get more gas, the “check engine” light turns off.

Since my truck is under warranty, I took it to the dealer (twice), and they told me it is “bad gas.” How can that be? I know I am a young chick, but I feel that they just don’t want to fix it. Could it be a bad knock sensor? They did say they checked everything, and it’s fine.

Can you do a paranormal investigation and tell me what my issue is? -- Gena

RAY: When I have bad gas, it doesn’t cause my “check engine” light to come on, Gena. But it does cause my houseguests to say “goodnight” early.

It could be bad gas, but if it’s happened three times and, I’m assuming, with gas from different gas stations, it sounds like they’re just trying to get rid of you. Or they don’t know how to fix this.

You can humor them by trying different gas if you haven’t already, but when that doesn’t help -- and before your warranty runs out -- go back to the dealer and tell them they need to look harder.

“P0324” is the code for a knock sensor malfunction. Bad gas (with too low an octane rating) could cause knocking, which might turn on the “check engine” light. But it’s also possible the knock sensor is faulty. And it may malfunction only under “load,” or high-stress conditions.

For example, if they tested the knock sensor at the dealership, it may have tested fine. But when you’re driving uphill at 65 mph, in 80-degree heat, pulling a 6,000-pound trailer, the sensor misbehaves.

So they should start by swapping out your knock sensor. It’s also possible your whole engine control module is bad. The knock sensor “reports to” the ECM. So that’d be next on my list.

Either way, this truck shouldn’t be knocking when you pull 6,000 pounds, since its towing capacity is more than twice that. So they’re going to have to make a more serious effort to fix this for you.

I’m going to guess that you’re pulling horses with this trailer, Gena. That would be perfect. Next time you go to the dealer about this, feed the horses first, then take them into the showroom with you, sit down and tell them “you’ll wait” while they figure it out. Good luck.

Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at

About the Author