# What causes rough idle at red lights?

**URL:** <https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567>\
**Category:** Maintenance/Repairs\
**Created:** [November 23, 2007, 1:34pm UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567 "2007-11-23T13:34:29Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![phillyrich](https://avatars.discourse-cdn.com/v4/letter/p/b19c9b/32.png) [@phillyrich](https://community.cartalk.com/u/phillyrich)\
**Post date:** [November 23, 2007, 1:34pm UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567/1 "2007-11-23T13:34:29Z")

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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.

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**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\
**Post date:** [November 24, 2007, 1:53am UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567/2 "2007-11-24T01:53:07Z")

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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.

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**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\
**Post date:** [November 24, 2007, 1:56am UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567/3 "2007-11-24T01:56:23Z")

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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?

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**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\
**Post date:** [November 24, 2007, 12:31pm UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567/4 "2007-11-24T12:31:05Z")

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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.

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**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\
**Post date:** [November 24, 2007, 1:29pm UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567/5 "2007-11-24T13:29:32Z")

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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.

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**Author:** ![Docnick](https://avatars.discourse-cdn.com/v4/letter/d/ecae2f/32.png) [@Docnick](https://community.cartalk.com/u/Docnick)\
**Post date:** [November 24, 2007, 11:41pm UTC](https://community.cartalk.com/t/what-causes-rough-idle-at-red-lights/7567/6 "2007-11-24T23:41:02Z")

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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.