# Rough Idle, loping, when engine is warmed up

**URL:** <https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067>\
**Category:** Maintenance/Repairs\
**Tags:** corolla, toyota\
**Created:** [June 29, 2013, 8:14am UTC](https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067 "2013-06-29T08:14:46Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Murphgeek](https://avatars.discourse-cdn.com/v4/letter/m/eb9ed0/32.png) [@Murphgeek](https://community.cartalk.com/u/Murphgeek)\
**Post date:** [June 29, 2013, 8:14am UTC](https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067/1 "2013-06-29T08:14:46Z")

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I have a 1993 Geo Prizm (Toyota Corolla) that idles roughly and lopes only when the engine is fully warmed up to operating temp. I changed the plugs, and wires are only 1 year old and seem to be in good shape. I suspected a vacuum leak, but have not been able to find one. Any thoughts about what could cause this problem?

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**Author:** ![knfenimore](https://avatars.discourse-cdn.com/v4/letter/k/9fc348/32.png) [@knfenimore](https://community.cartalk.com/u/knfenimore)\
**Post date:** [June 29, 2013, 10:11pm UTC](https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067/2 "2013-06-29T22:11:18Z")

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Either temp sensor for the engine or IAC & MAF need cleaning.

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**Author:** ![oblivion](https://avatars.discourse-cdn.com/v4/letter/o/3ab097/32.png) [@oblivion](https://community.cartalk.com/u/oblivion)\
**Post date:** [June 29, 2013, 10:16pm UTC](https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067/3 "2013-06-29T22:16:14Z")

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Bad EGR valve causing a vacuum leak when the ECM commands it to open?

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**Author:** ![bloody\_knuckles](https://avatars.discourse-cdn.com/v4/letter/b/ee7513/32.png) [@bloody\_knuckles](https://community.cartalk.com/u/bloody_knuckles)\
**Post date:** [June 30, 2013, 3:20am UTC](https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067/4 "2013-06-30T03:20:29Z")

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I agree with Oblivion. This vintage Toyota engine sometimes had EGR issues (clogged EGR tubes, bad EGR valves). Try cleaning the tubes out first and see if that helps.

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**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\
**Post date:** [June 30, 2013, 4:54am UTC](https://community.cartalk.com/t/rough-idle-loping-when-engine-is-warmed-up/80067/5 "2013-06-30T04:54:50Z")

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I think this car has an idle speed adjustment screw, right? First thing, make sure the idle adjustment screw is within its nominal limits. This symptom is common when the idle speed screw is turned to fix something that shouldn’t be fixed that way. Best of luck.