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Home >> Mercedes Benz >> 1988 >> 190D >> Repair and Diagnosis >> Engine Performance >> System >> Fuel Injection System - Diesel >> Testing >> Vacuum Idle Speed Increase

Vacuum Idle Speed Increase

NOTE: Before testing, check idle speed adjustment.
  1. With engine at idle, connect Vacuum Tester (116 589 25 21 00) to straight connection of thermovalve and energize with about 13 in. Hg. If idle speed does increase, go to step 2). If idle speed does not increase, check thermovalves. Ensure thermovalve has an open passage. Replace thermovalve as necessary.
  2. With engine stopped, check vacuum control unit for leaks. Energize vacuum tester with about 13 in. Hg. Vacuum value may drop approximately 3 in. Hg in one minute. If vacuum value is okay, go to step 3). If vacuum value is incorrect, check vacuum lines and connections for damage. Replace vacuum control unit as necessary.
    NOTE: Manufacturer recommends replacement of vacuum control unit in injection pump at a Bosch service station only.
  3. Check vent line for passage. Pull vacuum line from straight connection of thermovalve and connect with vacuum tester. Operate hand pump. Vacuum should not build up. If system test is okay, test is complete. If test is not okay, blow out vacuum line or replace vent filter.
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