Throttle Control System: Other Honda Civic II

CIVIC SI

Dashpot diaphragm chamber "A" slows the closing of the throttle valve during gear changes or deceleration. When throttle valve begins to close suddenly, its movement is slowed by the force of the spring in dashpot chamber "A" and the gradual increase of vacuum in dashpot chamber "B". A gradual increase in vacuum is caused by the restricted orifice in the manifold vacuum signal line.

Dashpot diaphragm chamber "B" is employed to increase airflow rate for fast idling at extremely low ambient temperatures. When dashpot control solenoid is activated by ECU during low ambient temperatures, manifold vacuum is not applied to dashpot diaphragm "B". This causes throttle to remain slightly open because throttle valve closing position is limited by throttle control rod.

CIVIC STD. & HF

When engine is idling, manifold vacuum is applied to dashpot diaphragm. This pulls the diaphragm rod so that the throttle valve is in the idle position. During cranking, vacuum is not present in diaphragm and internal diaphragm spring pressure pushes throttle valve open slightly.

Scheme 25

1. Start engine and warm to operating temperature (cooling fan comes on). Disconnect No. 6 vacuum hose at dashpot diaphragm. (Scheme 25)
2. Engine speed should increase to 2000-3000 RPM. If engine speed is out of specified range, perform «FUNCTIONAL TEST»(ref-94340-S31089944122001033000000) on Si models. On Std. and HF models, adjust by bending adjustment tabs. (Scheme 26)

Scheme 26

1. Start engine and allow to idle. Disconnect vacuum hose No. 6 from dashpot diaphragm and connect vacuum gauge to hose. (Scheme 25) If vacuum is not present, check hoses and connections. Check for blocked vacuum port at throttle body.
2. If vacuum is present, disconnect No. 22 hose from dashpot diaphragm and connect a vacuum gauge to hose. With engine coolant temperature less than 14°F (-10°C) and fast idle speed less than 1800 RPM, check for vacuum. If vacuum is not present, go to step 5). If vacuum is present, disconnect 4-wire dashpot control solenoid connector. (Scheme 27) Measure voltage between Black/Yellow (pos.) and Blue (neg.) wire terminals. If battery voltage is present, replace solenoid.
3. If battery voltage is not present, measure voltage between ground and Black/Yellow wire. If voltage is not present, repair open in Black/Yellow wire between 4-wire connector and fuse No. 14 or replace fuse. If battery voltage is present, turn ignition off. Connect System Checker Harness (07999-PD6000A) between ECU and ECU connector.
4. Check for continuity of Blue wire between ECU terminal B2 and 4-wire solenoid connector. If continuity does not exist, repair as necessary. If continuity does exist, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.
5. If vacuum was not present in step 2), warm engine to operating temperature (cooling fan comes on). Check for vacuum at No. 22 hose at dashpot diaphragm. If vacuum is present, system is functioning properly. If vacuum is not present, disconnect 4-wire solenoid connector.
6. If vacuum is still not present, replace solenoid. If vacuum is present, turn ignition off. Connect System Checker Harness (07999-PD6000A) between ECU and ECU connector. Check for continuity to ground in Blue wire between ECU terminal B2 and 4-wire solenoid connector. If continuity to ground exists, repair short to ground. If continuity to ground does not exist, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.

Scheme 27