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High idle on TBI engines

Discussion in 'Chevy Trucks' started by Alan, Jun 12, 2002.

  1. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    This is probably old news to most everybody here, but if you get a high idle condition on a TBI engine, check thoroughly for vacuum leaks. I've had an 89, 305 & now an 88, 350 which both developed a high (and increasing) idle speed. The 89 was traced to a bad gasket under the throttle body and just today I found a leak in the same area on the 88. Sprayed carb cleaner over vacuum connections and gasket areas until I got a change in RPM.

    Near as I can figure, a vacuum leak would cause irregular idle in a carburated engine but the computer sees a lean condition on a TBI and dumps in more fuel to compensate, raising speed as a result.