Vacuum hose misinstalled
Throttle body air leak
Intake manifold air leak
Evaporative Emission (EVAP) canister purge valve failure
Valve timing incorrect
Manifold Absolute Pressure (MAP) Sensor range/performance problem
Engine Light ON (or Service Engine Soon Warning Light)
The Positive Crankcase Ventilation (PCV) system reduces Hydrocarbon (HC) emissions. The PCV system recirculates unburned air/fuel mixture (blow-by gas) into the intake manifold so that it is drawn into the engine and burned, thus reducing HC. If the PCV hose comes off at idle with the throttle closed, the amount of air supplied to the engine is considerably more than the amount of air the idle control system supplies. The Powertrain Control Module (PCM) estimates the amount of air supplied to the engine while the throttle valve is fully closed, and if the estimated amount is more than the upper limit, it detects a malfunction and stores a Diagnostic Trouble Code (DTC).