What causes rough idle at red lights?

My old car runs fine, except that I have developed a rough idle at red lights.

Air filter is new, engine does not hesitate or backfire.

Providing any info as to type of car, year, engine, transmission (it makes a difference), mileage, etc. could help in throwing a few guesses out there.

Any Check Engine Light? Is it temperature or weather related? When was the last time the plugs and wires replaced? It is gasoline or diesel? What color is it? How long has it been like this? Any other issues or history on this car or truck?

Hey! I KNOW… I KNOW. If it’s a 1959 Studebaker with a flat head 6 cylinder and 1 bbl Carter carburator get the Knuder valve replaced.

Start down the list: use of an MAF spray cleaner, and an intake/throttle body spray cleaner; spark plugs; spark plug wires; fuel filter; repair shop.

Does it idle rough when you put it in Neutral too? Many cars idle a little rough when in gear with your foot on the brake, especially when they are warming up on.