Idle Speed, Checking

Idle Speed, Checking

Special tools and workshop equipment required







- VAS 5051 with VAS 5051/1

Requirements
- No leaks in exhaust system
- Coolant temperature at least 80 degrees C
- Electrical loads switched off (coolant fan must not run during test)
- Air conditioner switched off
- No pressure gauge connected
- Vehicles with automatic transmission: Selector lever set to P or N

NOTE:
- Idle speed is checked during basic setting of engine.
- During basic setting, the EVAP canister purge regulator valve -N80- is closed and the air conditioner compressor switched off.

Work sequence
- Connect vehicle diagnostic, testing and information system VAS 5051 and select vehicle system "01 - Engine electronics" from list. Engine must be idling. Connecting VAS 5051 Scan Tool
- Interrogate fault memory. There must not be any faults stored; if necessary eliminate faults and erase fault memory. After erasing fault memory, generate readiness code again. With Manufacturer's Scan Tool
- Leave engine idling.

CAUTION: Electric radiator coolant fan must not run.

Indicated on VAS 5051:







- From list -1- select diagnostic function "04 - Basic setting".

Indicated on VAS 5051:







1 Enter display group
- Use keypad -2- to enter "056" for "Display group number 056" and confirm by touching Q key.

Indicated on VAS 5051:







- Activate basic setting by touching key -A-.
- Check whether engine speed in display zone -1- (actual engine speed) is within permitted tolerance range.

Display Group 056:

NOTE:
- Engine speed in display zone 1 (actual) is actual engine speed.
- Engine speed in display zone 2 (specified) is a theoretical engine speed calculated by the engine control module.
- At idle, the engine control module always attempts to adjust actual engine speed to the specified engine speed.
- This means that at idle the actual engine speed must always roughly correspond to the specified engine speed.
- Display zones 3 and 4 are for information purposes and are of no relevance as regards checking of idling speed.
- Terminate function "04 - Basic setting" by touching <- key.

If reading does not match specification:
- Interrogate fault memory again.

Perform the following operations marked with a dot if idling speed is too high or too low/in the event of rough idling and no faults have been stored in fault memory:
- Check oxygen sensor learned values and control.
- Check for unmetered air in intake system.
- Check for permanently open EVAP canister purge regulator valve EVAP Canister Purge Regulator Valve - N80-, Checking.
- Adapt throttle valve control module. Programming and Relearning