Idle/Throttle Speed Control Unit: Testing and Inspection

DIS units are found on California cars with CIS fuel injection, and carbureted cars only.
1. If engine is difficult to start, does not start, or engine misfires or stalls, check the harness plug connections at the DIS.
a. Disconnect both harness plugs at the DIS (mounted on top of the ignition control unit) and connect them together.
b. Start the engine.
c. If engine troubles are eliminated, check the plug terminals.
NOTE: The DIS plugs are a common source of intermittent ignition problems. Before replacing the DIS, replace the terminal connectors and coat them with dielectric grease, and retest the system.
d. If the engine does not start, the DIS is probably not at fault.
2. If engine starts and runs, but idle speed varies, test the ignition advance capabilities of the DIS as follows:
a. Connect harness plugs to the idle stabilizer.
b. Connect a tachometer and a timing light to the engine.
c. Start engine and run at idle, noting ignition timing.
d. Switch ON all electrical consumers including A/C (if applicable).
3. If ignition timing does not advance when engine speed drops below 840 RPM, replace the DIS.