Volkswagen Workshop Service and Repair Manuals

Notes:

• ◆ Idling speed, ignition timing and CO content not adjustable.
• ◆ On vehicles08.95 ▸ with throttle valve control part J338 the idling speed is regulated to specification by the throttle valve positioner in conjunction with the DIS function.
• ◆ On vehicles ▸07.95 the idling speed is regulated to specification by the throttle valve potentiometer G69 and the idling stabilisation valve N71 in conjunction with the DIS function.
• ◆ CO content regulated by Lambda regulation. Faults in Lambda control are detected in self-diagnosis and stored in fault memory.

Special tools, testers, measuring instruments and auxiliary items required

• ◆ Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3

Check conditions

• ● Exhaust system between cylinder head and catalyst free of leaks
• ● Coolant temperature at least 85 °C.
• ● All electrical consumers, e.g. lights and rear window heating must be switched off
• ● If the vehicle is equipped with an air conditioner, this must be switched off.
• ● On vehicles with automatic gearbox selector lever in "P" or "N" position
• ● Throttle cable adjustment must be OK, checking:

=> Repair group 20; Removing and installing parts of fuel supply system; Adjusting throttle mechanism

Test sequence

• ‒ Connect fault reader V.A.G 1551 (V.A.G 1552). Start engine and select "Address word" 01 of engine control unit. When doing this the engine must be running at idling speed.
  (Connecting fault reader and selecting engine control unit .)
• ‒ Interrogate fault memory, if necessary, repair fault and then erase fault memory.
  => Page 01-13 , interrogating and erasing fault memory
• ‒ Then:
• ‒ Leave fault reader V.A.G 1551 connected.
• ‒ Continue running engine at idling speed.

• ‒ Press keys 0 and 4 for the function "Introduction of basic setting" and confirm entry with Q key.

Checking idling speed

• ‒ Press the ⇒key.

• ‒ Press keys 0, 0 and 1 for "Display group number 1" and confirm entry with Q key.

• ‒ Check whether the coolant temperature is above 85 °C in display zone 2.
• ‒ Check idling speed in display zone 1.
       Specification: 650...750 rpm1)

     1)     Up-to-date specifications:

=> Exhaust emissions test binder

Note:

During idling check the activated charcoal filter solenoid valve and the air conditioner are switched off and the Lambda regulation learning procedure is initiated.

• ‒ Press ⇒key.
• ‒ Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.

If the idling speed is not obtained:

Vehicles08.95 ▸

• ‒ Match the engine control unit to the throttle valve control part => Page 24-119
• ‒ Carry out test drive.
• ‒ Again interrogate the control unit fault memory.
• ‒ Repeat the idling check.

If the specifications are not obtained again:

• ‒ Check throttle valve control part
  => Page 24-37 .

Vehicles ▸07.95

• ‒ Check the idling stabilisation valve via final control diagnosis => Page 01-53 .
• ‒ Check throttle closing damper and its adjustment => Page 24-91 .
• ‒ Carry out test drive.
• ‒ Again interrogate the control unit fault memory.
• ‒ Repeat the idling check.
• ‒ Check specifications in display group 1
  => Page 01-65 evaluating measured value block.