Operation CHARM: Car repair manuals for everyone.

Idle Speed, Checking



IDLE SPEED, CHECKING

- Idle speed, ignition timing and oxygen sensor factor (CO content) are not adjustable.
- The idle speed is held to specification by altering the ignition timing. Digital Idle Stabilization (DIS) function.
- The position of the distributor housing has no influence on ignition timing.
- CO content is regulated by oxygen sensor control. Malfunctions in oxygen sensor control are detected by the On Board Diagnostic program and stored in Diagnostic Trouble Code (DTC) memory.

Special tools, testers and auxiliary items
- VAG 1551 Scan Tool (ST) with VAG 1551/3 adapter cable

Test conditions
- Engine oil temperature 80 °C (176 °F) minimum
- Electrical consumers switched off (radiator coolant fan must not run during the
check)
- Air conditioner switched off
- Exhaust system must be free of leaks
- No malfunctions stored in DTC memory. Refer to "On-Board Diagnostic". Testing and Inspection
- VAG 1551 Scan Tool (ST) connected

Test sequence
- Start engine and run at idle speed.
- Operate VAG 1551 scan tool taking into account the information on the display
- Press button -1- to select "Rapid data transfer" operating mode.
- Press buttons -0- and -1- to insert "Engine Electronics" address word 01.
- Press -Q- button to confirm input.
- Press -> button.
- Press buttons -0- and -4-to select "Basic Setting" function 04.
- Press -Q- button to confirm input

Indicated on display

Basic setting HELP
Input display group number XXX


- Press -0-, -0- and -1- to input display group number 001.
- Press -Q- button to confirm input.

Indicated on display (1, 2, 3 and 4 = Display fields)

Basic setting 1 ->
1 2 3 4


NOTE: In the "Basic Setting" function the EVAP canister purge regulator valve N80 is closed and the Malfunction Indicator Lamp (MIL) in the instrument cluster lights up.

CAUTION: Do not continue with the check until engine coolant temperature exceeds 80 °C (display field 2).

- Briefly increase engine speed (RPM) by pressing on accelerator pedal, then allow engine to run at idle speed for 2 minutes.
- Read values displayed for RPM, oxygen sensor factor and ignition timing.





- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06.
- Press -Q- button to confirm input.

If RPM specifications are not attained:
- Switch ignition off.
- Check accelerator pedal mechanism for ease of operation.
- Disconnect harness connector from Motronic ECM then reconnect.
- Carry out test drive, check DTC memory, and check idle speed again.