P1504moderate severityPowertrain
Idle Air Control Solenoid Circuit Intermittent
on 2018 Mazda MX-5 Miata 2.0L I4 · RWD
What this code means
The PCM has detected an intermittent electrical fault in the Idle Air Control solenoid circuit. The IAC solenoid connection is making and breaking contact, causing erratic idle speed behavior.
Symptoms
- Check Engine Light
- Erratic idle speed
- Idle fluctuates up and down
- Intermittent stalling
Common causes
- Loose IAC solenoid connector
- Corroded IAC wiring or pins
- IAC solenoid with intermittent coil fault
- Damaged wiring near engine vibrating loose
- PCM connector issue
Diagnostic steps
- Wiggle test IAC connector while monitoring idle speed
- Inspect IAC solenoid connector for corrosion or loose pins
- Test IAC solenoid resistance at various temperatures
- Check wiring for chafing or intermittent breaks
- Monitor IAC duty cycle for erratic changes
Repair notes
Repair the IAC connector or wiring; replace the IAC solenoid if it has an intermittent internal fault.
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