What this code generally means, its most common causes, and how serious it is.
TYPE: GENERICSYSTEM: IDLE AND SPEED
What does the code P0505 mean?
The idle air control system fine-tunes airflow (or the electronic throttle) to keep engine speed stable while stopped. This code, the most general in this family, flags a fault without specifying whether idle is too high or too low.
Common possible causes
A carbon-clogged throttle body— the most common cause, especially after mileage without cleaning.
A vacuum leak— lets in unregulated air.
A failing idle control valve or motor— no longer adjusts intake air correctly.
General severity
Generally minor — worth fixing
This code mainly shows up as an unstable or rough idle, most noticeable while stopped. Driving on the move usually remains normal.
⚠️This is still a general severity for this code, not a diagnostic for your car. Only a real read of your codes, with your mileage and vehicle history, can tell what's really going on.
Get a diagnostic for YOUR car
Connect a Bluetooth OBD2 reader and read your vehicle's real codes with Meca — free, no appointment, with causes ranked for your actual situation.
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Frequently asked questions
My engine shakes while stopped — is that related?›
That's a common symptom of this code — an unstable idle can feel like a slight shake while stopped.
Can cleaning the throttle body fix this?›
Often yes, when carbon buildup is the real cause — it's a routine maintenance step.
Can I drive normally with this code?›
Yes generally, the effect is mostly felt at idle, not during normal driving.