Idle Speed (RPM), Checking

Idle Speed (RPM), Checking

Special tools and equipment







- VAS5051 Vehicle diagnosis, testing and information system with VAS5051/1 Adapter

Requirements
- Exhaust system free of leaks
- Coolant Temperature at least 80 degrees C.
- Electrical consumers switched off (radiator coolant fan must NOT run during test)
- A/C switched off
- No pressure gauge connected

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

Work sequence

- Connect VAS5051 tester, Vehicle Diagnostic, Testing and Information System VAS 5051, Connecting and Selecting Functions and select vehicle system "01 - Engine electronics". Engine must run at idle during this.
- Check DTC memory. DTC Memory, Checking 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.

CAUTION: The electric coolant fan for the radiator must not be running.







Display on VAS5051:
- In selection -1-, click on diagnostic function "04 - Basic Setting".







Display on VAS5051:
1 - Enter display group. Max. input value = 255
- Select function "056" in button field -2- for "display group number 056" and press Q button to confirm input.







Display on VAS5051:
- Check whether engine speed in display field 1 (actual engine speed) is within permissible specified range.







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 information, but are not relevant for checking idle speed.







Display on VAS5051:

If specified value is obtained:
- End function "04 - Basic setting" by pressing <- button.

If specified value is not obtained:
- If DTC memory was erased, generate readiness code again. Generate Readiness Code

If idle speed is too high or low and there are no DTCs in the DTC memory, the following tests (marked with dots) must be performed:
- Check for false air in intake air system.
- Check throttle valve control module. Testing and Inspection
- Evaporative Emission (EVAP) canister purge regulator valve always open.
- Perform adaptation of throttle valve control module.

Significance of 5 digit indication of display group 056