Idle Speed Checking

Idle Speed Checking

Test conditions
- No leaks in exhaust system
- Coolant temperature at least 85 °C (185 °F)
- Electrical consumers switched off (radiator fan must not run during the check)
- A/C switched off
- Pressure gauge not connected
- Selector lever in position P or N (vehicles with automatic transmission)

Checking idle speed


NOTE:
- The idle speed cannot be adjusted.
- The idle speed is tested during the basic setting of the engine.
- During the basic setting of the engine the A/C compressor is automatically switched off and the EVAP canister purge regulator valve is closed.
- Check DTC memory. The DTC memory must be clear. If necessary, repair any malfunctions and erase the DTC memory. Switch off the engine, then start up again. Take vehicle for a test drive and check DTC memory again to make sure it is clear.
- Run engine at idle speed.
- Switch off A/C.
- Switch off rear window heating.
- Place selector lever in P or N position (automatic transmission).


CAUTION!
The electric radiator fan should not be running.


Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -4- to select function "Basic Setting" and confirm entry with -Q- button.

Indicated on display


Basic Setting
Input display group number XXX


- Press buttons -0- -5- and -6- to select "Display group number 056" and confirm entry with -Q- button.


NOTE:
- The value shown in display field 1 is the actual engine speed.
- The value shown in display field 2 (specified engine speed) is a theoretical value calculated by the engine control module.


Indicated on display: (1 - 4 = display zones)


System in Basic Setting 56 ->
1 2 3 4







- Check whether the engine speed shown in display zone 1 (actual engine speed) is within the specified tolerance range (650 to 720 RPM).
- When the engine is idling the engine control module tries constantly to adjust the actual engine speed so that it matches the specified value.
- This means that the actual engine speed when idling should always be approximately the same as the specified engine speed.
- Display fields 3 and 4 provide additional in formation which is not relevant when checking the idle speed.
- Press -> button.
- Press buttons -0- and -6- to select function "End Output" and confirm entry with -Q- button.
- If readout does not match specification, check DTC memory again.
- If DTC memory was erased, generate readiness code. Readiness Code, Generating

If the idle speed is too high or too low, or if the engine does not idle smoothly, and there are no malfunctions stored in the DTC memory, carry out the following tests (marked with dots):
- Check oxygen sensor learned values and oxygen sensor control.
- Check for un-metered air (air leaks) in the intake system.
- EVAP canister purge regulator valve constantly open, check. Testing and Inspection
- Adaptation of Throttle Valve Control Module.

Relevance of figures in 5-digit readout in Display Group 056