Here you can find informations about the settings of some important components

Throttle Switch Adjustment

Carefully remove the ruber protector and then the connector on the TPS. Connect an Ohmmeter between terminals 14 and 17. The value should be around “0” Ohm (continuity).

If the Ohm-Meter shows “endless”, reset the throttle switch, otherwise there is no idle signal and this no thrust cut-off. If there is no idle signal detected despite correct adjustment, the throttle switch must be replaced.If you manually raise the idle speed a little, the idle speed signal must be gone at the ohm meter (display endless). If the signal is not correct, there is a defect in the TPS.

VOLVO-GRUK.CH has a solution to this problem by allowing the printed circuit board to be replaced in the TPS. You can find all information about this under the topic throttle position switch.

Important Note! The CO-value at idle be set only, when the idle signal is shown correctly with continuity.

If the idle signal is missing, there is also an increased fuel consumption, because the overrun cut-off only works with idle signal and above 1800 rpm.

The TPS signal 1 (9 1/2 pulses) and TPS signal 2 (10 pulses) can be tested with the “Blue Bosch Box”, or by connecting an Ohm-Meter at Pin 9 or Pin 20 and Ground.

  • A simplified measuring method is also possible without the “Blue Bosch Box”.
  • Remove the fuel pump fuse (F5)
  • Switch on the ignition
  • Open the throttle valve slowly by hand.
  • Impulses to the injection valves can be heard by a short, clear click and are countable. (When closing the throttle valve, the pulses to the injection valves must not be audible; thrust cut-off).

If the clicking in between is more of a crackling sound, then the contact on the comb of the throttle possition switch will bounce and cause the jerking and dropouts in fuel delivery. The circuit board is worn out and the switch needs to be replaced or repaired. See throttle postition switch.

Trigger Contacts at Ignition Distributer

Check Trigger contacts at the bit (at the lower bottom of the ignition distributor):

  • These should not be oily and should work in perfect clean condition.
  • Cam lobes should be lubricated very slightly with a non-slip grease.

Finally, the CO-value must be checked or set on the control unit.

Setpoint: 2% CO

From model year 06.1971 on, the setting is made at the potentiometer at the control unit. Before that (1800 E with model year before 06.1970) the potentiometer is not available.

Turn the potentiometer completely to the right (clockwise) and then two clicks to the left (counter clockwise), the control measurement must now show 2% CO. If not: to the right = fat, to the left = lean.

If there is a significant deviation in the setting of the potentiometer or less than 2% CO when the potentiometer is clockwise, the entire injection system must be checked carefully. Something is wrong. Ask for diagnostiks

Idle Speed Adjustment

B20E/F: Loosen the lock nut of the conical screw under the air intake at the front of the intake manifold (air hose can be loosened). (SW 9/16 or 14mm)

Screw in/clockwise = lower speed

Unscrew screw/counterclockwise = higher speed


  • Manual gearbox: 850 to 900 rpm
  • Automatic gearbox: 750 to 800 rpm with gear engaged (Position D)

If the adjusting screw is screwed in as far as it will go, and the speed is still too high, this may have the following causes: 

  • The basic setting of the throttle valve is too wide open.

For adjustment see the following topic “Adjusting Throttle Position Switch (TPS)”.

Adjusting Throttle Position Switch (TPS)

Slightly loosen the two screws at the throttle position switch (the valve must be able to move freely)

Loosen the stop-screw of the throttle valve (counterclockwise) and close the throttle valve completely. Then screw in the stop screw until the trottle starts to open. From this point, screw in the stop screw a HALF turn further and tighten with the lock nut. Then reset the throttle switch. See topic “Throttle Switch Adjustment”.

More mistakes: 

  • The additional air slide does not close correctly.
  • Incorrect air in the intake system (collector seal, large sealing ring of the injection valves,
  • Wrong air at the pressure switch (Leaks) or in the supply line.
  • Too much pre-ignition or hanging centrifugal weights in the ignition distributor