Intake Manifold Runner Control Stuck Open (GM)
What does P1518 mean?
The P1518 code means the vehicle's onboard diagnostic system has detected: Intake Manifold Runner Control Stuck Open (GM). This is a moderate severity code.
Common Symptoms
- Reduced low-RPM torque
- Check Engine Light illuminated
- Poor acceleration from a stop
- Slightly rough idle
- Decreased fuel economy in city driving
Probable Causes (Ranked by Likelihood)
- Carbon deposits jamming the runner valve open Very High
- Broken intake manifold runner actuator High
- Disconnected vacuum hose to the actuator Moderate
- Torn vacuum actuator diaphragm Moderate
- PCM signal missing or faulty Low
Step-by-Step Diagnostic Procedure
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Inspect the intake manifold runner valve for carbon buildup or mechanical binding.
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Command the IMRC with a scan tool and check for proper valve movement.
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Check vacuum hoses to the runner actuator for leaks or disconnections.
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Apply vacuum to the actuator with a hand pump to test if the diaphragm holds.
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Verify the PCM control solenoid is receiving and passing the signal.
Frequently Asked Questions
What does 'stuck open' mean for the intake runner?
The intake manifold runners have valves that change the effective runner length. Stuck open means the short runner path is always active, which provides good high-RPM power but reduces low-RPM torque.
Is this the same as a DISA valve on BMW?
The concept is the same but the designs differ. GM uses intake manifold runner control while BMW calls their system DISA (Differentiated Intake System Adjuster). Both optimize intake runner length for performance.
Can carbon cleaning solve this?
If the valve is stuck due to carbon buildup, cleaning it can restore proper operation. Remove the intake manifold and clean the valves, pivot shafts, and passages with a suitable solvent.