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  1. #1

    Default need help with 88 k1500 and 89 c3500 Hi idle

    I have a 88 k1500 with a 5.7 tbi engine and a 89 c3500 with a 7.4 tbi engine . Both trucks have a hi idle problem.The 5.7 idles fine when cold then idles up after it warms up. The 7.4 idles hi at start up and never changes. I have replaced the temp sensor on both trucks and the iac on the 454. I dont know what to try next.

  2. #2


    Check for vacuum leaks

  3. Likes zuki82 liked this post
  4. #3


    Thanks. I did find a major vacume leak under the adapter plate for the throttle body. The high idle was caused by a miss adjusted cruise control cable. Got both fixed.

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