P1518
Intake Manifold Runner Control Stuck Open
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The P1518 is a Ford-specific code indicating that the Intake Manifold Runner Control (IMRC) system has detected that the runner plates are stuck in the open position. The IMRC system uses movable plates inside the intake manifold to change the effective runner length — shorter runners (plates open) optimize high-RPM airflow, while longer runners (plates closed) improve low-RPM torque. When the plates are stuck open, you lose the low-RPM torque benefit.
The most common cause in Ford vehicles is carbon buildup on the runner plates. Over time, oily carbon deposits from the PCV and EGR systems coat the butterfly plates and their bores, eventually causing them to bind or stick. This is especially common on the 4.6L, 5.4L, and 3.5L EcoBoost engines. In many cases, the plates can be cleaned with intake cleaner and a brush without removing the intake manifold, though a thorough cleaning may require removal.
If cleaning doesn't resolve the issue, the IMRC actuator (either electric motor or vacuum solenoid, depending on the model year) may need replacement. Check for broken linkage and worn bushings as well. While you can continue to drive with this code, you'll notice reduced torque at lower RPMs and slightly worse fuel economy. The engine will still perform adequately at higher RPMs since the plates are stuck in the high-flow position.
Severity
Symptoms
- •Check engine light is on
- •Reduced engine power, especially at low RPMs
- •Engine feels sluggish during acceleration
- •Rough or uneven idle
- •Decreased fuel economy
Likely Causes
Over time, carbon deposits from crankcase ventilation and EGR gases accumulate on the IMRC butterfly plates, causing them to stick in the open position.
The electric actuator or vacuum solenoid that controls the runner plates can fail electrically or mechanically, leaving the plates stuck open.
The mechanical linkage connecting the actuator to the runner plates can break, seize, or have worn bushings that prevent proper plate movement.
On vacuum-operated IMRC systems, a cracked vacuum hose or leaking diaphragm prevents the system from generating enough vacuum to close the runner plates.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Clean carbon deposits from the IMRC plates and intake manifold runners
- Replace the IMRC actuator motor or vacuum solenoid
- Repair or replace broken linkage and worn pivot bushings
- Replace cracked vacuum hoses in the IMRC vacuum circuit