Air Intake Control System: Other Honda Civic II

THROTTLE BODY

Throttle body is a single or 2-barrel side-draft type. The lower portion of throttle valve is heated by engine coolant which flows from cylinder head. Idle adjusting screw, which increase or decreases by-pass air, and canister purge port are located on top of throttle body. A throttle angle sensor is attached to primary throttle shaft to send throttle angle information to ECU.

A dashpot is used to slow closing of throttle valve as it approaches closed position during gear shifting or sudden deceleration. When throttle is fully closed, throttle valve linkage contacts throttle valve stop screw. This screw is factor set and is not adjustable.

DASHPOT CONTROL VACUUM SOLENOID (CIVIC Si)

ECU controls solenoid which regulates vacuum to outer side of idle speed dashpot based upon coolant temperature. When solenoid is energized, vacuum signal to dashpot is blocked. This causes spring pressure to slightly open throttle valve, allowing for cold fast idle. The inner side of idle speed dashpot controls throttle closure speed using spring pressure and an orificed (restricted) manifold vacuum signal. ECU controls outer side of diaphragm only.

ELECTRONIC AIR CONTROL VALVE (EACV)

All models are equipped with an Electronic Air Control Valve (EACV). When idle speed is reduced due to electrical or other loads on engine, ECU opens this valve to by-pass additional air into intake manifold. This additional air will allow idle speed to increase to maintain normal idle.

After coolant temperature has reached 104°F (40°C), this valve lowers fast idle speed in steps during engine warm-up. To prevent erratic running after engine first fires, valve is opened during cranking and immediately after starting which by-passes additional air into intake manifold.

FAST IDLE VALVE

A higher idle speed is needed to prevent erratic running during engine warm-up. This is accomplished on all models except Civic through use of a thermowax fast idle valve. When thermowax valve is less than 86°F (30°C), valve is open. When valve is open, additional air is allowed to by-pass throttle valve into intake manifold. When thermowax is hot, valve is closed. This operation is dependent solely upon coolant temperature. On Civic models, all idle speeds are controlled by the ECU, using the EACV (and dashpot solenoid on Civic Si).

Scheme 8

Scheme 9

Scheme 10

THROTTLE CABLE

1. Check that throttle cable operates properly with no binding or sticking. Check throttle cable free play at throttle linkage. Cable free play should be 0.40-0.50" (10-12 mm). If free play is not within specification, loosen lock nut and turn adjusting nut until free play is at specification. (Scheme 11)
2. With cable properly adjusted, check throttle valve to ensure it opens fully when accelerator is depressed. Check throttle valve to ensure it returns when accelerator is released.

Scheme 11

1. Start engine. Warm to operating temperature (cooling fan comes on). Disconnect canister vacuum hose from top of throttle body. Connect vacuum gauge to throttle body.
2. Check vacuum gauge when throttle is slightly opened from idle. Vacuum should be indicated on gauge. If gauge indicates no vacuum, check canister port for clogging. Clean with carburetor cleaner if necessary. Turn ignition off. Check for binding or sticking throttle linkage. Replace throttle body if excessive play exists in throttle shaft or if shaft is binding or sticking.

Scheme 12

DASHPOT SYSTEM

1. Slowly open throttle arm until dash pot rod is fully extended. Release throttle arm and measure time until throttle arm contacts stop screw. Time should be less than 2 seconds.
2. If time is over 2 seconds, replace dashpot check valve and retest. If rod does not operate, check for bound linkage, or for clogged check valve or vacuum line. If they are okay, replace dashpot.

Scheme 13

Scheme 14

1. Check by-pass valve shaft for binding, sticking and smooth movement. Ensure by-pass valve is in close contact with stopper when by-pass valve is fully open. Ensure by-pass valve is in close contact with full close screw when by-pass valve is fully closed. (Scheme 13)
2. Clean linkage and shafts with carburetor cleaner if fault is found. Start engine and allow to idle. Remove vacuum hose from by-pass control diaphragm and attach a vacuum gauge to hose. (Scheme 14) Check for vacuum. If vacuum is present, go to step 4).
3. If no vacuum is present, disconnect vacuum supply hose from by-pass control solenoid. Check for vacuum. If vacuum is present, proceed to step 6). If no vacuum is present, check vacuum line between solenoid and intake manifold. Repair as necessary.
4. If vacuum was present in step 2), increase engine speed to 5000 RPM and check vacuum gauge. If vacuum is not present, by-pass control system is functioning properly. If vacuum is present, disconnect 4 or 6-wire solenoid connector. (Scheme 15) If vacuum is now present, replace by-pass control solenoid valve.
5. If no vacuum is present with solenoid connector unplugged, turn ignition off. Connect System Checker Harness (07999-PD6000A) between ECU and ECU connector. Disconnect "A" connector from ECU only, not main harness. Check for continuity to ground on Yellow wire between ECU terminal A8 and 4 or 6-wire connector. If continuity exists, repair short to ground in Yellow wire. If continuity does not exist, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.
6. If vacuum was present at solenoid in step 3), disconnect 4 or 6-wire solenoid connector. (Scheme 15) Measure voltage between Black/Yellow (pos.) and Yellow (neg.) terminals. If battery voltage is present, replace by-pass control solenoid.
7. If no battery voltage was present in step 6), measure voltage between Black/Yellow terminal and body ground. If no battery voltage is present, repair open in Black/Yellow wire between connector and No. 11 (Accord) or No. 12 (Prelude) fuse or replace fuse.
8. If battery voltage was present in step 7), turn ignition off. Attach System Checker Harness (07999-PD6000A) between ECU and solenoid connector. Check for continuity of Yellow wire between 4 or 6-wire connector and ECU terminal A8.
9. If continuity does not exist, repair open in Yellow wire. If continuity is present, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.

Scheme 15

Civic Throttle Body Injection

1. With engine coolant temperature less than 160°F (70°C), disconnect vacuum hose from tandem valve control diaphragm. (Scheme 16) Connect vacuum gauge to hose. Start engine. If vacuum is present, go to step 3). If vacuum is not present, increase engine speed to 2000 RPM for automatic transmission or 3000 RPM for manual transmission.
2. If vacuum is not present, go to step 5). If vacuum is present, warm engine to operating temperature (cooling fan comes on). Slowly open throttle. If vacuum is present, tandem control system is functioning properly. If vacuum is not present, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.
3. Disconnect 2-wire connector from tandem control solenoid. (Scheme 17) If vacuum is now present, replace solenoid. If vacuum is not present, turn ignition off. Disconnect "B" connector from ECU. Check for continuity to ground on Orange wire.
4. If continuity exists, repair short to ground in Orange wire between ECU terminal B2 and 2-wire connector. If continuity to ground does not exist, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.
5. If vacuum was not present in step 2), disconnect 2-wire tandem control solenoid connector. (Scheme 17) Measure voltage between Black/Yellow (pos.) and Orange (neg.) terminal at 3000 RPM. If battery voltage is not present, go to next step. If battery voltage is present, remove solenoid valve and check port for blockage. If port is okay, replace solenoid.
6. Measure voltage between ground and Black/Yellow wire terminal. If voltage is now present, go to next step. If voltage is not present, repair open in Black/Yellow wire between 2-wire connector and No. 14 fuse.
7. Turn ignition off. Connect System Checker Harness (07999-PD6000A) between ECU and ECU connector. Check for continuity in Orange wire between ECU terminal B2 and 2-wire connector. If continuity does not exist, repair open in Orange wire.
8. If continuity does exist, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.

Scheme 16

Scheme 17

RESONATOR CONTROL SYSTEM

Note. Resonator system test procedures given specifically apply to Integra models. Information for other models was not available from manufacturer, however, procedures listed should be similar.

1. Start engine and allow to idle. Remove vacuum hose to resonator control diaphragm. Connect vacuum gauge. If vacuum is not present, go to step 3). If vacuum is present, increase engine speed to about 3000 RPM. If vacuum is still present, go to step 7). If vacuum does not exist, connect vacuum pump/gauge to resonator diaphragm. (Scheme 18)
2. Apply vacuum. If diaphragm linkage activates and vacuum holds, no problem exists in resonator system. If linkage does not move and/or diaphragm does not hold vacuum, replace diaphragm or repair binding linkage.
3. If vacuum was not present in step 1), disconnect lower vacuum supply hose at resonator solenoid. Check for vacuum. If vacuum is not present, check for blockage in hose or vacuum port, or disconnected hose.
4. If vacuum is present, disconnect 6-wire connector from resonator control solenoid. (Scheme 18) Measure voltage between Black/Yellow (pos.) and Red (neg.) terminals. If battery voltage is present, replace resonator control solenoid.
5. If battery voltage is not present, measure voltage between ground and Black/Yellow wire. If battery voltage is not present, repair open in wire between 6-wire connector and fuse No. 4 or replace fuse.
6. If battery voltage is present, turn ignition off. Connect System Checker Harness (07999-PD6000A) between ECU and ECU connector. Check for continuity of Red wire between ECU terminal A10 and 6-wire resonator solenoid connector. If continuity does not exist, repair Red wire as necessary. If continuity does exist, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.
7. If vacuum was present in step 1) with engine speed at 3000 RPM, disconnect 6-wire resonator solenoid connector. (Scheme 18) If vacuum is now present, replace solenoid. If vacuum is not present, turn ignition off. Disconnect "A" connector from ECU. Check for continuity to ground on Red ECU terminal A10 wire. If continuity exists, repair short to ground between ECU terminal A10 and 6-wire solenoid connector.
8. If continuity to ground does not exist in Red wire, substitute a known good ECU and retest. If symptom is rectified, replace original ECU.

Scheme 18