Stalls/Rough, Unstable or Incorrect Idle
SYMPTOM DESCRIPTION:
The engine runs unevenly at idle. If bad enough, the vehicle may shake. Also, the idle may vary in rpm (called "hunting"). Either condition may be severe enough to cause stalling. Engine idles at incorrect speed. Check the following systems and components.
COMPUTER INPUTS/OUTPUTS
ENGINE SPEED/REFERENCE SENSOR: Check for improperly positioned or damaged sensor. Check for damaged or missing teeth at the reference wheel. Refer to Crankshaft Position Sensor,
IDLE VALVE:
AIR FLOW METER:
OXYGEN SENSOR (O2) - Inspect sensor for silicon contamination from fuel, or use of improper RTV sealant. The sensor will have a white, powdery coating, and will result in a high but false signal voltage (rich exhaust indication). The Digital Motor Electronic (DME ) control unit will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
THROTTLE POSITION SWITCH/SENSOR: Improper adjustment.
COOLANT TEMPERATURE SENSOR: Refer to Coolant Temperature Sensor,
FUEL
FUEL INJECTOR BALANCE TEST: Poor spray pattern, clogged or stuck.
FUEL PRESSURE: Check fuel pressure and output volume.
IGNITION
SECONDARY IGNITION SYSTEM: Refer to Ignition Systems,
DME CONTROL UNIT: DME final output stages.
EMISSIONS
EVAPORATIVE SYSTEM: Test purge valve and charcoal canister operation.
PCV VALVE: Test for proper operation.
ENGINE
VACUUM LEAKS: Test for vacuum leaks at intake system.
BATTERY: Cables and ground straps should be clean and secure.
CRANKCASE AIR LEAKS: Check at dip stick seal, oil filler cap, front and rear engine oil seals.
A/C refrigerant pressure too high, overcharge or faulty high pressure switch.
MOTOR MOUNTS:
CYLINDER COMPRESSION:
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Friday, August 11th, 2006 AT 6:34 PM
