Checking idle speed and exhaust gas analysis

6-cylinder engines are equipped with automatic idle speed control.

There is no adjusting bolt, so there is nothing to adjust. Idle speed is only checked. Under correct test conditions (see below), the following idle speed must be obtained: 680 – 820 rpm (2.6 L engine) or 700 – 800 rpm (2.8 L engine). Otherwise:

PROCEDURE

Check all intake system components (piping, sealing gaskets) for leaks. Unmetered air entering the system can change idle speed so much that even the idle air control valve cannot compensate for it.

Read the fault memory at the workshop. There may be another fault in the system.

Test Conditions
PROCEDURE

The engine must be at normal operating temperature, and the fuel injection and ignition systems must be in good working order.

Next, switch off all electrical consumers in the vehicle.

The cooling fan must also not be running.

Disconnect both crankcase ventilation hoses and plug the hose ends.

Switch off the air conditioning.

Place the automatic transmission selector lever in position "N" or "P".

Warm up the engine to normal operating temperature (oil temperature at least 60 °C).

The replacement air filter element must be perfectly clean.

For CO analysis, no exhaust extraction device may be connected to the exhaust system.