Idle Mixture Check

Required Special Tool: 

MB991502: Scan Tool (MUT-II)

1. Before inspection, set the vehicle in the following condition:
   • Engine coolant temperature: 80 - 95°C (176 - 203°F)
   • Lights and all accessories: OFF
   • Transaxle: Neutral (P range on vehicles with A/T)
   CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
2. Connect scan tool MB991502 to the data link connector.
3. Check that the basic ignition timing is within the standard value.

   Standard value: 5° BTDC +/- 3° 

4. Start the engine and increase the engine speed to 2,500 r/min for 2 minutes.
5. Set the CO, HC tester.
6. Check the CO contents and the HC contents at idle.
   Fig 1: Connecting Scan Tool MB991502 To Data Link Connector

   Courtesy of DAIMLERCHRYSLER CORPORATION

   Standard value: 

   CO contents: 0.5 % or less 

   HC contents: 100 ppm or less 

7. If the CO and HC contents do not remain inside the standard value, check the following items:
   NOTE: Replace the catalytic converter when the CO and HC contents do not remain inside the standard value, even though the result of the inspection is normal for all items.
   • Diagnostic output
   • Closed-loop control (When the closed-loop control is carried out normally, the output signal of the heated oxygen sensor changes between 0 - 400 mV and 600 - 1,000 mV at idle.)
   • Fuel pressures
   • Injector
   • Ignition coil, spark plug cable, spark plug
   • EGR system and EGR valve leak
   • Evaporative emission system
   • Compression pressure