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  1. #1

    Default Persistent Loping Idle and Surging Acceleration

    Friends, I am desperate, I tried everything I know and more but I cannot find a solution to my Loping idle and surging acceleration on my '90 Sierra C1500, 5.7L TB. I I've replaced the IAC valve, TPS, MAP, EGR & Solenoid, ES Module & Knock Sensor, ECS, Ignition Module, Plugs & Wires, Dist. Cap & Rotor & Fuel Filter.

    Compression is 118psi to 120psi and fuel pressure 10psi, within the 9 to 13psi tolerance. I reset the IAC Valve by jumping the A & B terminals on the diag. connector,* turn to ignition to the on position, NOT START, wait a minute then disconnect the IAC Valve electrical connector. Then turn the ignition to the off position, remove the jumper from the diag. reconnect the IAC connector. Then start the engine and set the idle speed. (method from Chilton Manuel, different than ThirdGen article.)

    My COs is 160 but should be 20, my HCs is 2.95 but should be 2.00. Nox was 0.34 well below the exceptible 4.00

    My Injectors spray pattern seem right though the droplets size seems larger than I imagined, but uniform and smooth. The only relivant parts that I haven't yet replaced is the Injectors, Ignition Coil, Ignition Pickup Coil.

    I'm near my wits end, please help this desperate man regain some sanity.
    Sincerely xJohn Doex

  2. #2
    Sr. Engineer
    Join Date
    Oct 2010
    Indianapolis, In


    That thing should run like a new one. Could you describe in more detail about the surging acceleration?
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  3. #3


    When I drive it the response to the accelerator lags then it does in disconcerting surges.

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