Stalling, Rough, Unstable Or Incorrect Idle

Check fuel pressure.
Check throttle linkage and/or TP sensor for sticking or binding. Ensure throttle bore is free of foreign material.
Check ignition timing.
Check for leaking fuel injector(s) and connections.
Check for restricted air filter.
Check for open EGR valve at idle.
Check PCV valve operation.
Check for vacuum leaks.
Check HO2S for silicone contamination from fuel or improper RTV sealant.
Check for fuel in fuel pressure regulator hose, indicating a faulty fuel pressure regulator.
Check for excessive fuel additives.
Check knock sensor (KS) operation (if equipped).
Ensure the installed PROM and/or PCM is correct for that particular vehicle. Check with dealer for latest application information.
Check air injection system.
Check engine coolant temperature sensor for proper temperature-to-resistance values.
Check for correct charging system voltage.
Check canister purge system operation.
Check Idle Air Control (IAC) system operation (if equipped).
Check MAP sensor (if equipped) operation.
Check for high A/C pressure due to overcharge or faulty pressure switch.
Check power steering pressure switch and circuit operation.
Ensure battery cables are clean and tight.
Ensure engine compression is correct.
Check for throttle body tampering.
Check for restrictions in air intake.
Check for restriction in IAC passage.
Check for faulty TP sensor and circuit.
Check for faulty transmission range switch and circuit.
Check for improper PCM grounds.
Check ignition system and grounds.
Check valve timing.
Check for improper or worn camshaft.
Check engine compression.
Check for damaged or worn push rods, rocker arms, valve springs and camshaft lobes.
Check for sticking or leaking valves.
Check for faulty motor mounts.