Notes On Intermittents
Check for binding throttle linkage due to TV, cruise, throttle cables, TPS installed improperly or throttle shaft binding. Check for proper throttle return spring and throttle return spring installation.
Probe ECM pin "A7" to ground with a voltmeter. Manipulate wiring and connectors at closed throttle and watch for 5.0 volts, indicating an open from "A7" to ground. Manipulate wiring and connectors at open throttle and watch for zero volts, indicating short to ground on circuit No. 427.
NOTE:
The following step numbers refer to circled numbers on diagnostic chart. See Fig 1
. For circuit identification, see Fig 2
.
- ISC status should be "LO" with the plunger depressed. When released, plunger status should be "HI".
- Checks throttle shaft for throttle plates binding, weak or distorted throttle spring, cruise and TV cables binding throttle linkage and check TPS for proper installation.
- When ISC bottoms fully in retracted position, the throttle switch will open. ISC should be partially extended to control idle.
- Never connect a voltage source across pins "A" and "B" of ISC. Damage to throttle switch contacts will result.
- This step simulates throttle switch shorting pins "A" and "B" of the ISC. If status light indicates cycling, harness and ECM are okay. Fault is in ISC motor connector or ISC motor.
- Checks for 5-volt reference signal to ISC.
- 5-volt reference from ECM to ISC is open or shorted to ground.
- 5-volt reference is okay. Check for open circuit No. 1030 from ISC pin "B" to ground.