Suspect vacuum leak and or MAF sensor
Malfunction is detected when mixture ratio compensation amount is too large (mixture is too lean or too rich). Possible causes are:
Fuel pressure incorrect.
Defective Mass Airflow (MAF) sensor.
Lack of fuel (DTC P0171 or DTC P0174 only).
Intake air leaks (DTC P0171 or DTC P0174 only).
1. Start engine and let it idle. Check for exhaust air leaks before 3-way catalyst. Check for intake air leaks after MAF sensor. If any leaks are found, repair as necessary. If no leaks are found, go to next step.
2. Turn ignition off. Disconnect ECM harness connector.
Disconnect appropriate HO2S1 harness connector.
On bank 1, check continuity of White wire between HO2S1 harness connector terminal No. 1 and ECM harness connector terminal No. 91.
On bank 2, check continuity of White wire between HO2S1 harness connector terminal No. 1 and ECM harness connector terminal No. 92. Also, check circuit for short to ground and short to voltage. If problem is found, repair as necessary. If problem is not found, go to next step.
3. Check fuel pressure
Fuel pressure should be about 51 psi (350 kPa) at idle
If fuel pressure is not okay, repair fuel system as necessary.
Thursday, November 27th, 2008 AT 10:42 AM