P0505 code: Idle Air Control System Malfunction
P0505 means idle Air Control System Malfunction. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0505 means
The idle air control (IAC) system meters a small amount of air past the throttle to keep a smooth idle when your foot is off the gas. P0505 is a general fault in that system — the computer can't hold the idle where it wants. The most common cause is a carbon-clogged IAC valve or a dirty throttle body restricting that airflow; a vacuum leak or IAC wiring fault can also cause it. Cleaning the IAC valve and throttle body resolves a lot of these, often followed by an idle relearn.
P0505 symptoms
- Rough, unstable, or hunting idle
- Stalling at stops or when coming to a stop
- Idle that surges up and down
- Idle that dips when accessories switch on
- Check-engine light
What it costs to fix P0505
Typical range: $50–$450 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| IAC valve / throttle body cleaning | $8–$20 | ~0.3–1 hrs |
| Idle air control (IAC) valve | $30–$150 | ~0.3–1 hrs |
| Vacuum / intake leak repair | $10–$150 | ~0.5–2 hrs |
Cleaning is the cheap first step and frequently enough (do an idle relearn afterward). A replacement IAC valve is modest. A vacuum leak's cost depends on which hose or gasket leaks.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0505 for my exact vehicle →
How to fix P0505
Easy — basic tools, most owners can do this
- Check for obvious vacuum leaks
With the engine idling, listen for hissing and inspect vacuum hoses and the intake duct for cracks or loose clamps. A leak that lets in unmetered air can upset idle control all by itself — fixing one may clear the code without touching the IAC.
- Remove and clean the IAC valve
Unbolt the idle air control valve (usually two screws on the throttle body), and spray the pintle and passage with throttle-body cleaner until the carbon is gone. Heavy black buildup on the pintle is your confirmation that clogging was restricting the idle airflow.
- Clean the throttle body
While the IAC is out, clean the throttle bore and the back of the throttle plate with cleaner and a rag. A carbon ring around the plate restricts the same idle airflow the IAC depends on, so cleaning both gives the fix its best chance.
- Perform an idle relearn
Reassemble, then follow your vehicle's idle relearn procedure — often a specific sequence of key-on, idle time, and A/C on/off, though some cars need a scan tool. Skipping this can leave the idle hunting even after a good cleaning.
- Test the IAC circuit if the code returns
If P0505 comes back after cleaning, check the IAC connector for corrosion and measure the valve's winding resistance against spec. A valve that's clean but electrically dead, or wiring that's damaged, means replacing the valve or repairing the circuit.
DIY or shop? This is one of the most DIY-friendly codes there is: the cleaning, reassembly, and most idle relearn procedures need nothing beyond basic hand tools and a can of cleaner. A shop earns its money only if the code persists after cleaning and the fault turns out to be wiring or an elusive vacuum leak, where a smoke machine finds in minutes what guessing can't. Try the cleaning first — it resolves a large share of these.
Tools for the DIY steps: Throttle-body/IAC cleaner · Screwdrivers and basic socket set · Clean rags · OBD2 scanner to clear the code · Multimeter (for the electrical check)
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0505.
Start a case with P0505 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0505?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0505 on specific vehicles
The likely causes shift by model. We’ve written up the patterns we see most:
P0505: common questions
Can I drive with P0505?
Redline can't make that call from a code. A rough or stalling idle can dip or kill the engine at stops; get it cleaned or diagnosed soon, and promptly if it stalls in traffic.
Will cleaning fix P0505?
Often — carbon clogging the IAC valve or throttle body is the most common cause. Clean both and perform an idle relearn so the computer recalibrates. If it returns, the IAC valve may need replacing or there's a vacuum leak.
What's the difference between P0505, P0506, and P0507?
P0505 is a general idle-control fault; P0506 is idle too low; P0507 is idle too high. They overlap in causes (cleaning, IAC valve, vacuum leaks) but the high/low versions point you toward the direction of the problem.
How much does it cost to fix P0505?
Often cheap — cleaner and labor, plus an idle relearn. An IAC valve is modest; a vacuum-leak repair varies by location. Clean first before buying parts.
Symptoms that trigger P0505
Drivers who get this code often notice one of these. Each has its own causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0505 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0505 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.