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rough idle

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by therover87, Jan 4, 2002.

  1. therover87

    therover87 1/2 ton status

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    i have an 87 k5 and the idle is rough, i let it warm up and when it gets warm the idle is very rough, i have changed the o2 sensor, plugs, wires, cap, rotor, coil, egr valve, could it be a vacuum leak, and if so how do i check it, thanks.
     
  2. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    ooops.
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Being an 87 I would guess it's a TBI...

    Rene

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  4. Burbinator

    Burbinator 1/2 ton status

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    First off, does your "service engine soon" light illuminate briefly when you start the truck? Make sure the bulb works...

    Second, put the ECM into test mode by shorting pins "A" and "B" on the diagnostic connector to the left of the steering column under the dash. I believe the two pins are: "A", upper right corner of the connector and "B", directly to the left of "A" or directly below, I can't remember. Someone help me out here...

    Turn the ignition on. The "service" light should blink a code 12 (flash, pause, flash flash) to confirm operation, then any stored codes which can be deciphered with a Chilton's, Hayne's or factory manual. Each code, including code 12, will flash three consecutive times.

    That would be my first suggestion. If you have a vacuum leak, it may pop a code for the MAP sensor. Then you can use the old "garden hose in the ear" trick to isolate it. Or you may get something else from the ECM so you can go in that direction.

    Hope this helps!

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