Intake Air Control System (Prelude)

Intake control solenoid valve is located at right side of engine, under intake duct. See COMPONENT LOCATIONS . When engine speed is below 3970 RPM, PCM supplies ground to intake control solenoid. This opens intake control solenoid valve sending intake manifold vacuum to intake control diaphragm.

1. Start engine and allow to idle. Disconnect vacuum hose, located between intake control solenoid valve and intake control diaphragm, from upper port of intake control solenoid valve. See VACUUM DIAGRAMS article. Check for vacuum at open port of intake control solenoid valve. If vacuum does not exist, go to next step. If vacuum exists, go to step  7.
2. Reconnect vacuum hose to upper port of intake control solenoid valve. Disconnect vacuum hose from intake control vacuum tank. See VACUUM DIAGRAMS article. Check for vacuum at open hose of intake control vacuum tank. If vacuum exists, go to next step. If vacuum does not exist, check for blockage or vacuum leak between intake control vacuum tank and intake manifold.
3. Turn ignition off. Disconnect intake control solenoid valve 2-pin connector. Turn ignition on. Measure voltage between intake control solenoid valve connector terminals. If battery voltage does not exist, go to next step. If battery voltage exists, replace intake control solenoid valve.
4. Measure voltage between ground and intake control solenoid valve harness connector terminal No. 2 (Black/Yellow wire). If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Black/Yellow wire between intake control solenoid valve connector and No. 14 ECU (15-amp) fuse located in under-dash fuse/relay box. See WIRING DIAGRAMS article.
5. Turn ignition off. Reconnect intake control solenoid valve 2-pin connector. Turn ignition on. Using backprobe set, connect a fused jumper wire between PCM 32-pin connector "A" terminal No. 9 (Brown/Black wire) and terminal No. 25 (White wire). Go to next step.
6. If intake control solenoid valve does not click when jumper wire is connected, repair open in White wire between intake control solenoid valve and PCM 32-pin connector "A". See WIRING DIAGRAMS article. If intake control solenoid valve clicks when jumper wire is connected, substitute a known-good PCM and recheck. See SUBSTITUTING PCM in SELF-DIAGNOSTICS - INTRODUCTION article. If symptom or indication goes away, replace original PCM.
7. Increase engine speed to more than 4200 RPM. Check for vacuum at solenoid valve upper port. See WIRING DIAGRAMS article. If vacuum does not exist, go to step  9. If vacuum exists, disconnect intake control solenoid valve 2-pin connector. Check for vacuum again. If vacuum does not exist, go to next step. If vacuum exists, replace intake control solenoid valve.
8. Turn ignition off. Disconnect PCM 32-pin connector "A". See PIN VOLTAGE CHARTS article. Check for continuity between ground and intake control solenoid valve 2-pin harness connector terminal No. 1 (White wire). If continuity exists, repair short in White wire between PCM 32-pin connector "A" and intake control solenoid valve. See WIRING DIAGRAMS article. If continuity does not exist, substitute a known-good PCM and recheck. See SUBSTITUTING PCM in SELF-DIAGNOSTICS - INTRODUCTION article. If symptom or indication goes away, replace original PCM.
9. Apply vacuum to vacuum hose disconnected from intake control solenoid valve upper port. See VACUUM DIAGRAMS article. If vacuum holds, intake system is okay at this time. If vacuum does not hold, check vacuum hoses for proper connections or disconnected, cracked or leaking hoses. If vacuum hoses are okay, replace intake control diaphragm.