Idle Mixture Trouble Shooting

IDLE MIXTURE TROUBLE SHOOTING

Problem

Probable Cause

Rough Idle

Normal

High

Incorrect Ignition Timing, Faulty Ignition Components, Incorrect Valve Clearance, Defective EGR Valve, Leaking Intake/Exhaust Valves, Defective Cylinder

Rough Idle ⁽¹⁾

Low

High

Vacuum Leaks, Lean Mixture Causing Misfire

Rough Idle ⁽²⁾

High

Restricted Air Filter, Plugged PCV, Faulty Pressure Regulator, Clogged Fuel Return Line, Defective Coolant Temperature or Air Temperature Sensor, ECU, Fuel Injector, Cold Start Injector, TPS, Airflow Meter

⁽¹⁾	Fluctuating HC reading.

⁽²⁾	Black smoke from exhaust.