Federal

Fig. 28 Pneumatic High Idle Speed System Vacuum Schmatic:

NOTE: See Fig. 28 for a vacuum schematic of the pneumatic high idle speed system.

NOTE: To replace the high idle vacuum unit the injection pump must be removed from the vehicle. The replacement should only be done by an authorized Bosch dealer.

1. Hook up TDC impulse transmitter and engine analyzer to engine. Warm engine to normal operating temperature and check idle speed. If the idle speed is not 750 ±50 rpm, adjust the idle speed.
2. With engine at idle connect vacuum pump to straight connection of thermovalve and apply 500 mbar vacuum. Idle speed should increases approx. 100 rpm. If it does not, check the thermovalves. The thermovalve receiving vacuum from the brake booster check valve must be closed and the thermovalve with a "Y" connection must be open. If not, replace defective valve. Check vacuum lines according to vacuum line diagram.
3. With the engine stopped, test high idle vacuum unit for leaks. Apply 500 mbar vacuum with vacuum pump to high idle vacuum unit. The vacuum drop is not to exceed 100 mbar in 1 minute. If it does, check the vacuum lines and connections for damage. Replace fuel injection pump if no leaks are found.
4. Check vent line for restrictions. Pull vacuum line from straight connection of thermovalve (white vacuum line in diagram) and connect vacuum tester. Operate hand pump. If vacuum reading is not maintained, proceed with step 5. If vacuum reading is maintained, replace vent filter and blow out vacuum line.
5. Tee into horizontal connection of idle speed increase switchover valve and connect vacuum gauge. Run engine at idle speed, set Tempmatic temperature selector wheel to "MIN" position and turn on A/C system. The vacuum reading should be approx. 700 mbar and the idle speed should increase. If the vehicle passes the above tests, the pneumatic high idle speed system is ok. If the vehicle fails this test, proceed to step 6.
6. Check voltage at electrical connection to idle speed increase switchover valve. If voltage is present, check vacuum lines for leaks. If no leaks are found, replace switchover valve.