P0505: How to Diagnose & Fix — Idle Air Control System Malfunction
8 vehicles · 7 makes · $20-$700 repair
How to diagnose and fix P0505: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Nissan Cube · 2009–2014
Owners report Cubes that suddenly stall or stop pulling while driving, sometimes at highway speed, often with no warning lights at first. When the engine actually dies, power steering and brake assist are lost and the car can be hard to restart. Owner reports do not point to one cause. On 2009-2010 Cubes, many "stalls" turned out to be the CVT transmission: the engine revs but the car coasts, or the car goes into fail-safe mode. One owner reported the CVT codes P1778, P0868, P0725 and P0746, and several owners had the transmission replaced more than once. Other owners describe true engine shut-offs that dealers could not find a cause for. A 2012 owner had repeated shut-offs in hot weather; a shop recommended a relay, and the dealer did a computer update, but the car shut off again. A 2009 owner's mechanic suspected an overheating fuel pump. No stalling-specific service bulletin is listed for the 2010 Cube. A 2011 bulletin, SB-11-016A, covers RPM fluctuation at highway speed on 2009-2010 Cubes.
Common Symptoms
- Engine shuts off without warning while driving, sometimes at highway speed
- Loss of power steering and brake assist when the engine dies
- Engine revs but the car slows or will not move (CVT loss of drive or fail-safe mode)
- Check engine light may come on only later, or not at all
- Difficulty restarting after stalling
How to Fix
1) Note what happens when the car stalls. Did the tachometer drop to zero and the engine shut off, or did the engine keep running or rev while the car stopped moving? Revving without moving points to the CVT, not the engine. 2) Have the codes read right after it happens, including stored and pending codes. CVT codes one owner reported were P1778, P0868, P0725 and P0746. Check the CVT fluid level too, because one dealer found it overfilled. 3) If RPM rises and falls at steady highway speed on a 2009-2010 Cube, ask a Nissan dealer about bulletin SB-11-016A (RPM fluctuation on the highway). 4) If the engine truly dies with no codes, ask the shop to check the fuel supply and the relays while the fault is happening, especially in hot weather. Owners report that dealers often find nothing when the car is running normally. Coverage: Nissan extended CVT coverage on 2003-2010 CVT-equipped models to 10 years or 120,000 miles, but that time limit has now passed for every 2009-2010 Cube, and 2011 and later model years were outside it. Cost: owners report paying or being quoted about $2,935 to $4,500 for a CVT replacement. One 2012 owner was quoted about $460 for a relay and about $740 for a transmission computer.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Nissan crankshaft position sensor 23731-1VA0A
2009-2014 Cube 1.8L on the live fitment table; confirm VIN and connector/current supersession.
- Genuine Nissan camshaft position sensor 23731-EN22A
2009-2014 Cube 1.8L on the live fitment table; confirm VIN/current supersession.
- Genuine Nissan electronic throttle body 16119-9SE0A
Confirm VIN/core terms and complete all required electronic-throttle learning.
- Genuine Nissan spark plug 22401-JD01B
Quantity four; verify VIN, plug specification and gap-handling instructions.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipClean the throttle body with CRC Throttle Body Cleaner every 30,000 miles — this prevents carbon buildup that causes stalling.
- WarningStalling at highway speeds is extremely dangerous. If it happens more than once, do not drive until diagnosed.
Sources for this issue (6)
- 2009 Nissan Cube power train complaints (CarComplaints)owner-reports
- 2010 Nissan Cube power train complaints (CarComplaints)owner-reports
- 2009 Nissan Cube fail safe mode complaints (CarComplaints)owner-reports
- 2012 Nissan Cube engine stalls/shuts down while driving (CarComplaints)owner-reports
- 2010 Nissan Cube technical service bulletins (CarComplaints)tsb-list
- Extended powertrain warranty on CVT-equipped Nissan vehiclesnews
Volkswagen GTI · 1990–1999
The 8v/16v cars (including the 2.0 8v ABA) use an idle stabilizer valve to control idle air. It gums up internally with oil vapor and carbon over time, causing a low, hunting, or rough idle, especially when cold, and occasional stalling at stops. A cracked PCV hose or other vacuum leak produces similar symptoms and should be checked alongside it.
Common Symptoms
- Low or hunting idle, worse when cold
- Occasional stalling at stops
- Rough idle that improves after warm-up
- Idle surge
How to Fix
Remove and clean the ISV with electronics/MAF cleaner and let it dry, or replace it if resistance is out of spec (roughly 12.5 ohms outer-to-center, ~25 ohms outer-to-outer). Also inspect PCV hoses and vacuum lines for the same symptoms.
Sources for this issue (2)
Mazda 626 · 1993–1999
A very common driveability complaint on the 626 is an unstable idle that surges, dips, or stalls at stops, most often caused by a sticking or dirty idle air control (IAC) valve and, on higher-mileage cars, leaking intake manifold gaskets that create unmetered vacuum leaks (the gasket often leaks on the underside where it is not visible from above). The problem is worsened by carbon buildup in the throttle body. It affects both the FS I4 and KL V6, and because these are age/mileage-driven wear items rather than a single defect, it shows up across the whole 1990s run.
Common Symptoms
- Surging or hunting idle
- Stalling at stops or when coming to a stop
- Rough idle when cold
- Hesitation and weak acceleration
- Check-engine light
How to Fix
Clean or replace the IAC valve, clean the throttle body, and inspect/replace the intake manifold gasket if a vacuum leak is confirmed (smoke or carb-cleaner test). Check all vacuum lines first. These fixes are inexpensive parts with modest labor and typically restore a stable idle.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- CRC 05379 Carburetor and Throttle Body CleanerOEMCRC 05379
Clean a confirmed deposit-restricted throttle body during diagnosis Fitment/availability: Live priced Add to Cart page identifies CRC 05379 for carburetor/throttle-body and intake-part cleaning. Follow the label and protect sensors, coat…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
Honda Civic · 1996–2005
Toyota 4Runner · 1996–2002
Find P0505 by make
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P0505 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0505 mean?
P0505 stands for "Idle Air Control System Malfunction." P0505 indicates a malfunction in the idle air control (IAC) system, which manages how much air bypasses the throttle plate to keep the engine idling smoothly at the correct RPM. On older systems this is a dedicated IAC valve/motor; the computer uses it to raise idle for cold starts, A/C load, or accessory load. When the system can't maintain the target idle, you may get a high or low idle, surging, rough idle, or stalling — especially at stops or when cold. The cause is usually a dirty or failed IAC valve, but vacuum leaks and electrical faults are common too.
What are the most common causes of P0505?
The most common causes of P0505 are: Dirty or carbon-clogged idle air control valve, Failed IAC valve motor or stuck pintle, Vacuum leak in the intake system, Dirty throttle body or sticking throttle plate, Wiring or connector fault in the IAC circuit, Faulty PCV system causing unmetered air, PCM/ECM control fault. The specific cause varies by vehicle.
How much does it cost to fix P0505?
Repair costs for P0505 range from $20 to $700, depending on the vehicle and root cause.
Which vehicles are affected by P0505?
Au7o has documented P0505 across 8 vehicle models from 7 manufacturers: Ford, Honda, Mazda, Nissan, Toyota, Volkswagen, Volvo.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.