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Thread: idle problem

  1. #1

    Default idle problem

    1990 GMC Burb 350 TBI auto

    To start with, I love this war wagon...the wife does too! Now, on to the problem.

    The check engine light has been coming on and going off once and a while. No odd symptoms while the light is on.

    The other day, the check engine light comes on, then goes off.Nothing out of the usual happens while light is on.

    I park, come back 15 minutes later, the motor is on high idle,motor warm and tapping the throttle does not bring it down.

    I get on the freeway and I notice that the tranny torque converter will not upshift (lock) to its final gear, 1st,2nd,3rd, OD then TC locks.

    I get home, check all the vacuum lines etc, all is well. I start it up, and it idles just fine.I'm assuming that the torque converter issue has something to do with the high idle.

    Bizarre??????? Hmmm.Is there a way to check codes without taking it to a dealer? where can i get a fault code list?

    thanks for any help in advance.

    Last edited by warwagon; 11-11-2008 at 08:33 PM. Reason: spelling

  2. #2


    Take the air cleaner off and clean the throtle body and the idle air control motor with carb cleaner. Sounds like the IAC motor is sticking.

  3. #3
    Master Mechanic
    Join Date
    Oct 2008
    Brandon, FLA
    Blog Entries


    Yes you can read the codes if it has stored them. This is a OBD1 system and if you ground terminal a/b on the scan plug before turning the key on, then turn on the key and the CEL(check engine light) will flash 3 times(normal before it displays the code(s) stored, if the there are any.
    For example if you have a code 32 the light will flash 3 times first, then 2 times second for the #32. If it has no codes stored, then it will flash 1 time then 2 times for code #12, normal operation.
    You can get the codes from a Haynes/Chiltons manual for the OBD1 system.
    Also, get some good throttle body cleaner and do clean it, along with the IAC as stated. But you may also check to see if the EGR is dirty. I am not sure on this if its electronic(5 wire plug) attached to it. If so, get a new gasket and clean it as well. It has a pindle on it that opens and closes and can get stuck if dirty. Before removing it disconnect the negative cable, this will help not to have electrical issues with it.
    You also can clean the pindle with a pencil eraser if its not blackened and needs spray to clean. Let it dry real well before re-installing.


  4. #4

    Default idle problem

    Thanks. I'll try both of those and hopefully she'll be running good again.

  5. #5


    Read the below thread and it will tell you how to pull the codes and where the terminals are. The computer is trying to tell you what is wrong so check it and see.

    99 K 1500 Suburban
    78 Silverado Big 10 w/factory 454
    00 S-10 Blazer
    1976 Trans Am
    1980 Honda CB900 Custom

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