Idle Speed: Testing and Inspection

Special tools and equipment







- VAS5051 with VAG 5051/1
or
- VAG 1551 with VAG 1551/3A

Test conditions
- Exhaust system free of leaks
- Engine coolant temperature less than 80 °C
- Electrical consumers switched off (radiator fan must NOT run during test)
- A/C switched off
- Pressure gauge not connected
- Vehicles with automatic transmission: selector lever in P or N


NOTE:
- Idle speed cannot be adjusted.
- Idle speed is checked during Basic Setting of the engine.
- During Basic Setting, the Evaporative Emission (EVAP) canister purge regulator valve (EVAP valve - N80 -) is closed and the A/C compressor is switched off


Test sequence
- Check DTC memory. There must not be any DTCs stored, repair malfunctions if necessary, erase DTC memory, switch engine off and start again, road test vehicle and check DTC memory again as a control measure.
- Let engine continue to run at idle.


WARNING!
Engine coolant fan must not come on during test.


When indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -4- to select "Basic Setting" and press -Q- button to confirm input.

When indicated on display:


Basic Setting Q
Input display group number XXX


- Press buttons -0-, -5- and -6- to select "display group number 056" and press -Q- button to confirm input.

Indicated on display:


Basic Setting 56 ->
1 2 3 4


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

Display Group 56:

NOTE:
- Engine speed in display field 1 (actual engine speed) is the current engine speed.
- Engine speed in display field 2 (specified engine speed) is a theoretical engine speed calculated by the ECM.
- At idle, the ECM always attempts to adapt the engine speed (actual) to the specified engine speed (specified).
- This means that the engine speed (actual) must always approximately match the engine speed (specified) at idle.
- Display fields 3 and 4 provide in formation, but are not relevant for checking idle speed.


If specified value is obtained:
- Press -> button.

Indicated on display (function selection):


Rapid data transfer HELP
Select function XX


If specified value is not obtained:
- Check DTC memory again.
- If DTC memory was erased, readiness code must be re-generated.

If idle speed is too high or low and there are no DTCs in DTC memory, the following tests must be performed
- Un-metered air in intake air system, checking. Refer to "Intake Air System, Checking For Leaks (Un-Metered Air)", Testing and Inspection
- Check throttle valve control module.
- Evaporative Emission (EVAP) canister purge regulator valve always open, checking.
- Perform adaptation of throttle valve control module.

Significance of 5 digit display of display group 056

Display Field 4: