Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P1078: Intake Manifold Runner Control System Malfunction (High Rpm)
2004 Acura 3.5RLSECTION DTC P1078: Intake Manifold Runner Control System Malfunction (High Rpm)
WARNING: This page is about a different car, the 2003 Acura RSX. However, it is still accessible from the selected car via links, so may be relevant.
- Perform ECM/PCM reset procedure. See ECM/PCM RESET PROCEDURE/CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.
- Start engine and hold at 3000 RPM, with no load (in park or neutral), until cooling fan comes on. Increase engine speed to 5000 RPM. If DTC P1078 is set, go to next step. If DTC is not set, problem is intermittent. System is okay at this time. Check for poor connection(s) or loose wire(s) between Intake Manifold Runner Control (IMRC) solenoid valve 2-pin harness connector and ECM/PCM 24-pin "B" harness connector. See Figure .
- Disconnect vacuum hose from IMRC valve and connect vacuum gauge. See Figure . Increase engine speed to 5000 RPM. If vacuum is present, go to next step. If vacuum is not present, go to step 7 .
- Turn ignition switch off. Disconnect IMRC solenoid valve 2-pin harness connector. Start engine. Increase engine speed to 5000 RPM, then measure voltage between IMRC solenoid valve 2-pin connector terminals No. 1 and 2. If battery voltage is not present, go to next step. If battery voltage is present, replace IMRC solenoid valve.
- Measure voltage between ground and IMRC solenoid valve 2-pin harness connector terminal No. 1 (Black/Yellow wire). If battery voltage is present, go to next step. If battery voltage is not present, check No. 4 ACG fuse (10-amp) in under-dash fuse/relay box. If fuse is okay, repair open in Black/Yellow wire between IMRC solenoid valve and No. 4 ACG fuse (10-amp).
- Turn ignition switch off. Disconnect ECM/PCM 24-pin "B" harness connector. Connect fused jumper wire between ground and IMRC solenoid valve 2-pin harness connector terminal No. 2 (Red/Blue wire). Check for continuity between ground and ECM/PCM 24-pin "B" harness connector terminal No. 22 (Red/Blue wire). If continuity is present, update ECM/PCM or substitute with known-good ECM/PCM. If symptom or indication goes away, replace original ECM/PCM. If continuity is not present, repair open in Red/Blue wire between ECM/PCM 24-pin "B" harness connector terminal No. 22 and IMRC solenoid valve 2-pin harness connector terminal No. 2.
- Turn ignition switch off. Connect vacuum gauge to IMRC valve and apply vacuum. See Figure . If IMRC valve holds vacuum, go to next step. If IMRC valve does not hold vacuum, replace IMRC valve.
- Disconnect IMRC valve position sensor 3-pin harness connector. Measure resistance between IMRC valve position sensor 3-pin connector terminals No. 2 and 3 while applying vacuum to IMRC valve. If about 9500 ohms is present, update ECM/PCM or substitute with known-good ECM/PCM. If symptom or indication goes away, replace original ECM/PCM. If resistance is not as specified, replace IMRC valve assembly.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.