Check Engine Light

I tried to call in to your show Jan 08, 2011, but your switchboard operator, Hough Geeves Akrap wouldn?t pick up the phone.

What prompted me to call was a listener with a Check Engine Light problem. I also experienced the problem early winter this year with a 1998 Plymouth Breeze that I have owned since 2004. So far it has been resolved by going up to medium grade octane gasoline.

My problem seemed to be temperature related. When the temperature first dropped below 28, the engine idle was rough and labored as if something mechanically was out of balance. But when I accelerated or gently reeve the engine, there was no missing or roughness to the engine. Buy the second day the Check Engine light came on. I sparingly drove the car for 4 miles the next day. Two days later when the temperature rose above 30, within 15 minutes of another quick errand, the light went out.

The end of the next week the temperature dropped below 28 again and rough idling and the Check Engine light came on again. Later in the week when the temperature rose above 30 the light went out while I was driving.

Logically this ruled out any mechanical problems with the engine; valves, rings, pistons.

Thinking the lower temperatures reduced the gasoline burning thoroughly,

I have been buying regular gasoline from a regional gas station chain. So I switched to a national brand gasoline station (Shell), went up to middle level Octane, and bought a bottle gasoline treatment and ran it through 1 tank of gas when I had the opportunity to drive 200 miles over a weekend trip. The rough idle, the Check Engine light have not returned even though the temperature is now consistently below 28. That was a month ago. Most of my diving is in town 3 miles to work. But I do regularly make a single 200 mile round trip once a month. A full tank of gas for the month of daily driving and the 200 mile trip.

The first time it happened over a 3 day weekend, so I scheduled an appointment with the mechanic the next Monday. By then the light was out, and all they could offer me was, ?yes the history log did show the light came on, but not why, it could have been a piece of carbon on the sensor, that will be $100.?

But still can not make the logical connection between low air temperature, engine idle and higher octane gasoline retarding combustion.

Could you explain more thoroughly what a higher octane gasoline actually does for the engine. From my understanding, higher octane retards combustion to remedy gasoline igniting too so. Does higher octane gas burn at a higher temperature? ?. Does it cause the gasoline to burn more completely, helping to remove carbon.

Mel Davis

Springfield, IL

217 525-0027

If you want to send comments/questions to Tom & Ray this isn’t the spot. There is a link to email them. This is just a discussion board full of stooges like me and to the best of my knowledge none of the people who post here are Tom or Ray in disguise.

There’s a good chance that what happened with your check engine light and the gasoline and system cleaner and all of that was all basically coincidence. The next time the light comes on take it to a chain-type auto parts store (Autozone, Advance, …). They will read your error codes for free. Write down exactly what the codes are (format: P1234) and you can post them here for advice.

You’ve mostly got the story correct with octane level (it just resists combustion more/burns at a higher temp). For cars that don’t require high octane gasoline, putting “premium” in them does nothing for the car (not even cleaning carbon). It shouldn’t be called “premium” - it should just be called high octane. Sometimes if your car has some kind of problem that causes knock/ping higher octane gas can help. But it won’t solve whatever the underlying problem is.