P1078
Intake Manifold Runner Control System Malfunction (High RPM)
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The P1078 code is a Honda-specific code indicating the Intake Manifold Runner Control (IMRC) system is malfunctioning at high RPM. While P1077 flags a problem at low RPM, P1078 indicates the system cannot properly reconfigure the intake runners for high-RPM airflow. At higher engine speeds, the IMRC system shortens the effective intake runner length to allow more air volume into the cylinders, which is critical for peak horsepower.
When this system fails at high RPM, the engine may feel noticeably sluggish during hard acceleration or highway merging. You will likely still be able to drive the vehicle safely, but performance will be reduced. The code is often triggered by the same components as P1077 — vacuum leaks, a stuck butterfly valve, or a faulty solenoid — but specifically when the system fails to transition at higher speeds.
Diagnosis should start with a visual inspection of the vacuum lines and the IMRC solenoid. If the vacuum lines are intact, manually test the runner valve for free movement. Carbon cleaning of the intake manifold can resolve sticking valves. If these steps don't resolve the issue, the solenoid or its wiring may need replacement. This is a manageable DIY repair with basic tools.
Severity
Symptoms
- •Noticeable loss of power at higher RPM
- •Reduced acceleration during highway driving
- •Check Engine light illuminated
- •Engine feels sluggish above 3000 RPM
- •Slightly higher fuel consumption
- •Flat or dull engine response when pressing the accelerator hard
Likely Causes
The IMRC butterfly valve may be stuck in the closed (low-RPM) position due to carbon buildup or mechanical wear, preventing it from opening at high RPM.
The solenoid controlling the runner valve may not be energizing properly at high RPM, leaving the valve in the wrong position.
A broken or detached vacuum hose prevents the IMRC actuator from receiving the signal to change runner position at higher engine speeds.
Damaged wiring or corroded connectors between the ECM and IMRC solenoid can prevent the high-RPM actuation command from reaching the valve.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace cracked or disconnected vacuum lines to IMRC system
- Clean or replace stuck intake manifold runner butterfly valve
- Replace faulty IMRC solenoid valve
- Inspect and repair wiring and connectors in the IMRC circuit