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Generic gasoline powertrain DTC / Idle speed control

P0505: Idle control system malfunction

The controller detected an idle-control system malfunction under its monitoring conditions.

Generic definition
P0101
P0507

Likely cause paths · unconfirmed

A possible intake, throttle, or idle-air condition

Air leakage, deposits, or control movement can affect idle speed; the code does not identify a part to replace.

  • Note cold versus warm idle and whether the engine stalls.
  • Record recent battery, throttle, or intake service.

A possible idle-control signal or electrical condition

Command, feedback, or voltage conditions may contribute and require vehicle-specific testing.

  • Save related voltage, throttle, and air-flow codes.
  • Do not adjust the throttle stop or disconnect sensors.

Likely causes and repair directions are general, conditional orientation. The SAE citation supports the generic DTC definition only; it does not validate these causes, tests, repairs, or fitment to a particular vehicle.

Conditional likely repairs

A code describes a monitored condition; it does not prove a failed part. Use these directions only after confirming the cause.

If confirmed: A possible intake, throttle, or idle-air condition

If inspection confirms an intake or throttle condition, correct it with the approved procedure and complete any required relearn.

Evidence to confirm

  • The leak or throttle condition is confirmed by inspection/test.
  • Idle control stabilizes through the prescribed relearn/verification.

If confirmed: A possible idle-control signal or electrical condition

If electrical or control tests isolate a signal or supply fault, repair that cause and retest commanded idle operation.

Evidence to confirm

  • Circuit and command/feedback checks identify the fault.
  • The idle monitor passes after repair.

Guided evidence checks

  1. 01

    Record what happened

    Note when the warning appeared, what the vehicle was doing, and any recent service or change. Do not deliberately recreate an unsafe symptom.

  2. 02

    Make only a safe visual check

    Record whether the engine stalls or the idle changes with electrical load. Keep clear of moving parts and do not adjust throttle stops.

  3. 03

    Preserve scan-tool evidence

    Qualified technician

    Save code status, freeze-frame, and available idle command/feedback data.

  4. 04

    Confirm the system path

    Qualified technician

    A qualified technician should check for intake leaks, throttle/idle control operation, and electrical supply using OEM specifications.

Code-specific symptom note

  • Code-specific symptoms are not verified by the cited definition. Record the driver’s actual observations separately.

This generic code reference is not an OEM procedure, does not confirm that a DTC applies to a particular make/model/engine, and is not a repair diagnosis. Follow vehicle-specific service information or consult a qualified technician.