Idle Mixture Check

1. Before inspection, set the vehicle to the following conditions:
- Engine coolant temperature: 80 - 95° C (176 - 203° F).
- Lights and all accessories: "OFF".
- Transmission: Neutral (P range for A/T).
2. After turning the ignition switch to "OFF", connect scan tool MB991502, or equivalent, to the data link connector.
3. Check to be sure that the basic ignition timing is at the standard value. The standard value is 2° - 8° BTDC.
4. Start the engine and race it at an engine speed of 2,500 RPM for two minutes.
5. Connect a CO and HC tester.
6. Check the CO contents and the HC contents while the engine is idling.
Standard value:
CO contents: 0.5% or less.
HC contents: 100 PPM or less.
7. If the concentrations are outside the standard values, check the following items.
- Diagnostic output
- Closed loop control

NOTE: If closed loop control is being carried out normally, the heated oxygen sensor output signal will vary between 0 - 400 mV and 600 - 1,000 mV while the engine is idling.

- Fuel pressure
- Injectors
- Ignition coil, spark plug cables and spark plugs
- Evaporative emission control system
- Compression pressure

NOTE: If the results of the checks for all items are normal but the CO and HC concentrations still exceed the standard values, replace the three-way catalyst.