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Home >> Mazda >> 1997 >> MX-5 Miata Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0505 - Idle Control System Malfunction >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

  1. Inspect all applicable harness connectors. Repair as needed. Turn ignition on. Access ECM harness connector. ECM is mounted to bulkhead, behind passenger seat. Using voltmeter, backprobe applicable ECM harness connector. Measure voltage between ground and terminal No. 4Q.
  2. Voltage should be about 1 volt with engine off or about 4.8 volts with engine idling at normal operating temperature. If voltage is within specification, go to step 6). If voltage is not within specification, go to next step.
  3. Disconnect IAC valve harness connector. Ensure ignition is on. Measure voltage between ground and terminal "A" on IAC valve harness connector. If battery voltage is present, go to next step. If battery voltage is not present, check for open or short in White/Red wire between IAC valve and main relay.
  4. Turn ignition off. Disconnect ECM harness connectors. Check continuity of Blue/Orange wire between terminal No. 4Q on ECM connector and terminal "B" on IAC valve harness connector. Repair as needed. If continuity exists, go to next step.
  5. Check continuity between component terminals on IAC valve. If continuity exists, go to next step. If continuity does not exist, replace IAC valve.
  6. Erase DTC. See CLEARING CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC is present, replace ECM. If DTC is not present, intermittent poor harness connection may have caused DTC to originally set.
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