The idle air control (IAC) system signal is cutting in and out. The IAC valve regulates the amount of air bypassing the throttle plate to control engine idle speed.
Find certified mechanics near you who can diagnose and repair P0509.
For informational purposes only. Diagnostic trouble codes are starting points for diagnosis, not definitive answers. Always consult a certified mechanic for proper diagnosis and repair. Estimated costs vary by vehicle, location, and shop rates.