DEFINITION:
Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal.

Perform careful visual and physical check as described at the beginning of Section "B".
Perform "Diagnostic Circuit Check."

• CHECK
  • Ignition wires for shorts or faulty insulation.
  • Ignition system for moisture, dust, cracks, burns, etc. Spray plug wires with fine water mist to check for shorts.
  • For possibility of misfiring, crossfiring, or cutting out under load or at idle. If present, refer to the "Ignition System Check" Chart in Section "C4."
  • Secondary ignition voltage output with J 26972 (ST-i 25) spark tester or equivalent.
  • Ignition coil connections.
  • ECM and ignition system for faulty grounds.
  • Proper operation of EST See Section "C4".
  • Spark plugs. Look for wear, wetness, cracks, improper gap, burned electrodes, and heavy deposits.
  • Spark plugs for correct heat range. Fuel for poor quality, "stale" fuel, and water contamination.
  • Fuel system for restricted filter or improper pressure. Use CHART A-7.
  • Injectors for leakage. Pressurize system by energizing fuel pump through the under-hood fuel pump test connector.
  • EGR operation. Use Code 32 chart.
  • For vacuum leaks at intake manifold gasket.
  • Idle Air Control system. Use Code 35 chart.
  • Electrical system voltage. IAC valve will not move if voltage is below 9 volts or greater than 17.8 volts. Also check battery cables and ground straps for poor contact. Erratic voltage will cause the IAC valve to change its position, resulting in poor idle quality.
  • PCV valves for proper operation by placing finger over inlet hole in each valve end several times. Valve should snap back. If not, replace valve. Ensure that valve is correct part. Also check PCV hoses.
  • Canister purge system for proper operation. Use CHART C-3.
  • PROM for correct application. (Consult Service Bulletins).
  • Throttle shaft or TPS for sticking or binding. TPS voltage should read less than 1.25 volts on a "Scan" tool with the throttle closed.
  • MAP sensor output. Use CHART C1-D and/or check sensor by comparing it to the output on a similar vehicle, if possible.
  • Oxygen sensor for silicone contamination from contaminated fuel or use of improper RTV sealant. The sensor will have a white, powdery coating and will cause a high but false signal voltage (rich exhaust indication). The ECM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
  • Coolant sensor for a shift in calibration. Use Code 14 or Code 15 chart. Vehicle speed sensor (VSS) input with a "Scan" tool to make sure reading of VSS matches that of vehicle speedometer. See "Special Information" in Section "6E".
  • A/C relay operation. A/C should cut out at wide open throttle. Use CHART C-10
  • P/N switch circuit on vehicle with automatic transmission. Use CHART C-1 A.
  • Transmission torque converter clutch operation. Use CHART C-8.