Hesitation, Sag, Stumble

Definition: Momentary lack of response as the accelerator is pushed down. Can occur at all car speeds. Usually most severe when first trying to make the car move, as from a stop sign. May cause the engine to stall if severe enough.
^ Perform careful visual check as described at start of Symptoms. Testing and Inspection
^ Fuel pressure should be a steady 40 to 50 psi (276 to 345 kPa) at key "ON", engine "OFF". With the engine running, fuel pressure should be 32-38 psi and should increase with engine load. Also check for contaminated fuel. If fuel system pressure is not in this range, see Chart A-4B. Related Tests, Information and Procedures
^ Check MAP sensor for leaks or restrictions at the upper intake manifold MAP port. Tee a vacuum gage into the vacuum hose at the fuel pressor regulator. The gage reading and parameter ED02 should be approximately the same and respond quickly to changes in engine load.
^ Check for fouled cracked, or defective spark plugs or spark plug wires. Observing a scope pattern under load provides a good test.
^ Remove rocker covers. Check intake manifold bolt torque. Check for bent push rods, broken or weak valve springs. Check cam lift. Repair as necessary.
^ Check for correct PROM number (parameter ED99) Also check Service Bulletins for latest PROM.
^ Check TPS for binding or sticking.
^ Check ignition timing. See Emission Control Information label.
^ Check for proper operation of EGR system.
^ Perform an injector balance test:
^ Select ECM override ES04 "Injector".
^ While in the injector override select ECM Data ED11 "RPM".
^ Run engine at 1500 RPM with steady throttle.
^ Select each injector (1-8) and disable fuel (Push "Cooler" button) while observing ECM parameter ED11.
^ Check any injector that does not decrease engine RPM by at least 100.
^ Check for open HEI ground, circuit #453.
^ Check canister purge system see Chart C-3 for proper operation. Chart C-3 Canister Purge Diagnosis
^ Check for carboned or sticking valves.
^ Check for restricted exhaust or catalytic converter.
^ Check for binding primary or secondary throttle valves which stay open.
^ Check for ECM codes present. Refer to ECM Trouble Code Diagnosis for diagnosis if any codes are present. Testing and Inspection