Speed Control Operation Is Intermittent

1. Check when intermittent operation occurs. If intermittent operation occurs when vehicle is at cruising speed, proceed to step 2. If intermittent operation occurs when operating control buttons or turning steering wheel, proceed to step 8.
2. Check all system vacuum lines for tight connections, cuts or kinks. Check that there is at least 2.5 inches Hg of vacuum supplied to servo. If vacuum is satisfactory, proceed to step 3. If not satisfactory, service vacuum supply as needed.
3. Disconnect vacuum hose at servo end, then the vacuum reservoir line at check valve and plug open valve port. Apply 18 inches of vacuum to hose at servo end. If vacuum holds, proceed to step 4. If vacuum does not hold, replace check valve and repeat step 3.
4. Check that dump is closed when brake pedal is not depressed. Apply 18 inches of vacuum to dump valve. If vacuum can be pumped and held, proceed to step 5. If vacuum cannot be pumped and held, replace or adjust valve as necessary.
5. Disconnect reservoir vacuum line at check valve, then apply 18 inches of vacuum to open end of line. If vacuum holds, proceed to step 7. If vacuum does not hold, proceed to step 6.
6. Disconnect vacuum line from reservoir port and plug open end, then apply 18 inches of vacuum to other end of line disconnected from servo check valve. If vacuum holds, replace reservoir and repeat step 4. If vacuum does not hold, replace reservoir vacuum line.
7. Perform servo tests. If tests are satisfactory, proceed to step 8. If tests are not satisfactory, replace servo.
8. Perform control switch and circuit test. If test results are satisfactory, substitute amplifier with known good amplifier and proceed to step 9. If test results are not satisfactory, repair circuits or replace horn pad assembly as necessary. When replacing horn pad assembly, clean or service copper brushes and steering wheel ring.
9. If system operation is satisfactory, replace amplifier.