Engine Hesitates Or Stumbles On Acceleration

Check intake manifold vacuum. Vacuum should be more than 17.7 Hg at idle.
Check air filter element.
Ensure ECM terminal voltages are okay. See PIN VOLTAGE CHARTS article.
Verify Throttle Position (TP) sensor has correct adjustment and resistance value. See ADJUSTMENTS article.
Ensure fuel system pressure is correct.
Check ignition timing.
Check mass airflow sensor. See SYSTEM/COMPONENT TESTS article.
Check for restricted exhaust system.