# What causes a car engine to idle rough and miss?

**URL:** <https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922>\
**Category:** Maintenance/Repairs\
**Tags:** eldorado, cadillac\
**Created:** [October 11, 2009, 4:17am UTC](https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922 "2009-10-11T04:17:04Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![oldsfan](https://avatars.discourse-cdn.com/v4/letter/o/e0b2c6/32.png) [@oldsfan](https://community.cartalk.com/u/oldsfan)\
**Post date:** [October 11, 2009, 4:17am UTC](https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922/1 "2009-10-11T04:17:04Z")

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This car is a V8, always serviced  
  
  
  
 Plugs and wires changed, O2 sensor changed, distributor new, premium gas used, injector cleaner used – still rough idle and miss Thanks!  
  
  
  
 Any ideas? 1990 Cadillac 4.5 liter 99K

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**Author:** ![budd2049](https://avatars.discourse-cdn.com/v4/letter/b/77aa72/32.png) [@budd2049](https://community.cartalk.com/u/budd2049)\
**Post date:** [October 11, 2009, 5:20am UTC](https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922/2 "2009-10-11T05:20:17Z")

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I’m assuming a new cap and rotor were part of the distributor replacement.

Has a compression check been performed? Perhaps one of the valves is burned or not sealing properly.

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**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\
**Post date:** [October 11, 2009, 10:46am UTC](https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922/3 "2009-10-11T10:46:59Z")

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When was the last time the fuel filter was replaced.

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**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\
**Post date:** [October 11, 2009, 1:27pm UTC](https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922/4 "2009-10-11T13:27:35Z")

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Compression test.  
Check for leaky EGR valve.

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**Author:** ![hd72mm](https://avatars.discourse-cdn.com/v4/letter/h/9fc29f/32.png) [@hd72mm](https://community.cartalk.com/u/hd72mm)\
**Post date:** [October 11, 2009, 8:17pm UTC](https://community.cartalk.com/t/what-causes-a-car-engine-to-idle-rough-and-miss/37922/5 "2009-10-11T20:17:44Z")

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Look for vacuum leak