Possible Causes & Corrections

Check for restricted exhaust system. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in the BASIC TESTING article.
Check for bent push rods, broken valve springs or worn camshaft lobes.
Check ignition wires for short or faulty insulation.
Check distributor cap (if equipped) for moisture, dust or cracks. Finely mist spark plug wires with water to check for shorts.
Using Spark Tester (J-26792), check for adequate spark at spark plugs.
Check ignition system for faulty grounds.
Ensure EST wiring harness is not routed too close to ignition wiring. EST wiring harness routed too close to ignition wiring may cause induced voltage signals.
Check ignition coil connections.
Remove spark plugs, and check for incorrect heat range, wear, cracks, wetness, improper gap or heavy deposits.
Check for poor quality or contaminated fuel.
Check for improper fuel pressure.
Ensure EGR valve is not stuck open.
Check PCM for proper ground circuits.
Ensure TP sensor does not stick or bind. TP sensor voltage should be less than 1.25 volts at idle.