Idle Speed, Checking

Idle Speed, Checking

Special tools, testers and auxiliary items required

• Vehicle diagnostic, testing and information system ( VAS 5051)

• Adapter (VAS 5051/1)

Requirements

• No leaks in exhaust system

• Coolant temperature at least 80 °C.

• Electrical devices switched off (coolant fan must not run during the test).

• Air conditioning switched off.

• Pressure gauge not connected.

• Vehicles with automatic transmission: Selector lever in position P or N.

• The idle speed (RPM) cannot be adjusted.

• The idle speed (RPM) is tested during the basic setting of the engine.

• During basic setting, the Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80) is closed and the air conditioning compressor is switched off.

Work sequence

- Connect vehicle diagnostic, testing and information system (VAS 5051) and select vehicle system "01 -Engine electronics" in selection. Refer to => [ VAS5051, Connecting and Selecting Functions ] VAS 5051, Connecting and Selecting Functions. Engine must be running at idle.

- Check DTC memory. Refer to => [ DTC Memory, Erasing ] DTC Memory, Erasing. There must not be any DTCs stored. If necessary, repair any DTCs and erase DTC memory. After erasing DTC memory, generate readiness code. Refer to => [ Readiness Code, Generating ] Readiness Code, Generating.

- Leave engine idling.

CAUTION!
The electric coolant fan should not be running.

Display on (VAS 5051):





- Under - 1 - select diagnostic function "04 - Basic setting".

Display on (VAS 5051):





1. Enter display group

- Enter "056" for "display group number 056" in zone - 2 - and confirm entry by pressing Q button.

Display on (VAS 5051):





- Activate basic setting by pressing A button.

- Check whether engine speed (RPM) in display zone - 1 - (actual speed) is within permitted tolerance range.





• The engine speed (RPM) in display zone 1 (actual speed) is the actual engine speed.

• The engine speed (RPM) in display zone 2 (specified speed) is a theoretical value calculated by the engine control module.

• At idle, the ECM always tries to adapt the actual engine speed (RPM) to the desired (specified) engine speed (RPM).

• This means that the actual engine speed (RPM) must always approximately match the specified engine speed (RPM) at idle.

• The display zones 3 and 4 are there for information but are irrelevant to the control of the engine at idle.

- Exit function "04 - Basic setting" by pressing arrow button.

If specified value is not obtained:

- Check DTC memory again. Refer to => [ DTC Memory, Erasing ] DTC Memory, Erasing.

- If DTC memory has been erased, generate readiness code. Refer to => [ Readiness Code, Generating ] Readiness Code, Generating.

If the idle is too high or too low and there are no DTCs recorded in the DTC memory, perform the following tests:

• Check intake air system for unmetered air. Refer to => [ Intake Air System, Checking for Leaks ] Testing and Inspection.

• Check Throttle Valve Control Module (J338). Refer to => [ Throttle Valve Control Module, Checking ] Throttle Valve Control Module, Checking.

• Check to see if Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80) is continuously held open => [ , checking ] Testing and Inspection.

• Perform adaptation of Throttle Valve Control Module (J338). Refer to => [ Throttle Valve Control Module, Adapting ] Throttle Valve Control Module, Adapting.

Significance of 5 digit indication of display group 056