P0505 on 2008-2015 Scion xB: Idle Control System Causes and Fixes

What's Unique About the 2008-2015 Scion xB

The most important thing to know about the 2008-2015 Scion xB is that it does NOT have a separate Idle Air Control (IAC) valve like the first-generation xB or many other vehicles from this era. Instead, idle speed is managed directly by the Electronic Throttle Control System (ETCS), which makes tiny adjustments to the main throttle plate. Many owners and even some generic guides will mistakenly suggest cleaning or replacing a non-existent IAC valve, leading to confusion. The problem almost always lies with the electronic throttle body assembly itself, which gets contaminated due to the 2AZ-FE's known oil consumption issue.

Symptoms You May Notice

• Check Engine Light is on
• Engine stalls when coming to a stop or when idling
• Idle speed is too high (e.g., 1200-2200 RPM)
• Idle speed is too low or rough, sometimes causing vibration in drive
• Erratic or fluctuating idle RPM, may bounce 4-5 times before setting the code
• Difficulty starting the engine, may require pressing the gas pedal
• Surging idle when coasting with the clutch in

Most Likely Causes

1. Dirty Electronic Throttle Body 🔴 High Probability → Shop Fuel Injection Throttle Body The 2AZ-FE engine is known for an oil consumption issue, detailed in Toyota TSB S-SB-0024-11. This problem, caused by piston ring design, leads to excessive oil vapor being routed through the PCV system and deposited as heavy carbon and oil residue in the intake and on the throttle plate. This buildup physically restricts the throttle plate's movement, preventing the fine adjustments needed for idle control.
   How to confirm: Remove the air intake hose from the throttle body. Visually inspect the throttle bore and the edges of the throttle plate for a thick, black, sticky layer of carbon. The backside of the plate is often dirtier than the front.
   Typical fix: Remove the throttle body, clean it thoroughly on both sides with specialized throttle body cleaner and a soft cloth or brush, and reinstall with a new gasket. 🎬 Watch: How to easily clean your throttle body to fix a rough idle. An idle relearn procedure is required afterward. Some owners report needing to clean it multiple times if the first attempt is not thorough enough.
   Est. part cost: $10-$25 for cleaner and a new gasket.
2. Vacuum Leak 🟡 Medium Probability Rubber vacuum hoses and intake gaskets become brittle and crack with age and exposure to engine heat. The PCV hose that connects the valve cover to the intake air tube is a particularly common failure point.
   How to confirm: With the engine running, listen for distinct hissing sounds around the intake manifold, PCV valve, and vacuum lines. You can also carefully spray short bursts of carburetor cleaner or brake cleaner around suspected areas; a change in engine idle indicates you've found the leak. A professional smoke test is the most definitive method.
   Typical fix: Replace the cracked hose (the PCV hose, OEM part #12261-28180, is a common culprit) or leaking gasket.
   Est. part cost: $10-$50 for hoses or gaskets.
3. Failed Electronic Throttle Body Assembly ⚪ Low Probability → Shop Fuel Injection Throttle Body
   How to confirm: This is typically diagnosed after a thorough cleaning does not resolve the issue and no vacuum leaks are present. The internal motor or position sensor has failed. One user on ScionLife reported replacing the throttle body solved a vibration issue but the P0505 code persisted, indicating a potential issue with the replacement part or wiring. A buzzing or stuttering sound from the throttle body motor when the pedal is pressed can also indicate failure.
   Typical fix: Replace the entire throttle body assembly. It is recommended to use an OEM or Aisin (the original manufacturer) part for best results.
   Est. part cost: $150-$400 for aftermarket, $350-$500 for OEM.

Rare But Worth Checking

• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is extremely rare. It should only be considered after a new throttle body has been installed, all wiring has been checked, and no vacuum leaks are present, yet the code persists. A shop diagnosed this as the last possible step for a 2014 xB after extensive troubleshooting. ECUs rarely fail on their own; it is almost always a sensor or mechanical problem.
• Obstructed Accelerator Pedal: A floor mat bunched up under the accelerator pedal can prevent it from returning to the fully closed position, which the ECM may interpret as an idle control fault.

Diagnosis Steps

1. Scan for other DTCs. If other codes are present, address them first.
2. Inspect for Vacuum Leaks: Listen for hissing noises from the engine bay. Pay close attention to the PCV hose running from the valve cover to the intake duct, as it is a common failure point. Check all other vacuum lines connected to the intake manifold for cracks or disconnections.
3. Inspect and Clean the Throttle Body: Disconnect the negative battery terminal. Remove the air intake duct from the throttle body. Visually inspect for heavy carbon buildup. If dirty, remove the four 10mm bolts holding the throttle body, disconnect the electrical connector, and clamp the two small coolant lines to prevent coolant loss before disconnecting them. 🎬 See this walkthrough for removing and deep cleaning the throttle body. Clean the throttle body thoroughly off the engine, focusing on the plate edges and bore.
4. Reinstall Throttle Body: Use a new gasket (OEM Part #22271-75070 or equivalent) when reinstalling the cleaned throttle body to prevent new vacuum leaks.
5. Perform Idle Relearn Procedure: After reconnecting the battery, the ECM's memory is cleared. A specific relearn procedure is required. Start the engine and let it warm up completely. Then, let it idle for 10-15 minutes without touching the accelerator or turning on any accessories like A/C or lights. Some variations exist, but allowing a long, uninterrupted idle is the key.
6. Test Drive: Drive the vehicle under various conditions (city, highway) to confirm the idle is stable and the code does not return.
7. If the problem persists after cleaning, re-check for vacuum leaks with a smoke test. If none are found, the issue may be a faulty throttle body assembly itself or a deeper electrical problem.

Parts You'll Likely Need

• Electronic Throttle Body Assembly (OEM #22030-0H031) — This is the most common cause of P0505. A thorough cleaning often fixes the issue, but if the internal motor fails, the entire assembly must be replaced.
  Trusted brands: Aisin (OEM), Dorman, Hitachi, Standard Motor Products
  OEM price range: $350-$500
  Aftermarket price range: $150-$300
• Throttle Body Gasket (OEM #22271-75070) — Must be replaced whenever the throttle body is removed to prevent vacuum leaks. It is a cheap part that ensures a proper seal.
  Trusted brands: Toyota (Genuine), Fel-Pro, Mahle, Victor Reinz
  OEM price range: $5-$15
  Aftermarket price range: $4-$10
• PCV Hose (Ventilation Hose) (OEM #12261-28180) — This specific hose is a common point for cracks and vacuum leaks on the 2AZ-FE, which can cause or contribute to the P0505 code.
  Trusted brands: Toyota (Genuine)
  OEM price range: $15-$25
  Aftermarket price range: $10-$20

Technical Service Bulletins (TSBs) & Recalls

• S-SB-0024-11 (Rev2, Nov 2015) - '2AZ-FE Engine Oil Consumption Repair Procedure': Details the repair for excessive oil consumption by replacing piston assemblies on affected 2008-2015 xB models. This is the underlying issue that causes the throttle body contamination leading to P0505.
• S-SB-0031-14 - '2AZ-FE Engine Oil Consumption Inspection Procedure': Outlines the official dealer procedure for verifying if a vehicle suffers from the excessive oil consumption issue, which is a prerequisite for the repair covered in S-SB-0024-11.

Platform-Specific Known Issues

• The root cause of the dirty throttle body is often the 2AZ-FE engine's excessive oil consumption problem. Toyota issued TSB S-SB-0024-11 (later revised and expanded) for 2008-2015 xB models, acknowledging that faulty piston assemblies can lead to high oil consumption. This oil gets into the PCV system and contaminates the throttle body, directly leading to the P0505 code.

Mechanic-Grade Diagnostic Values

• Throttle Control Motor Resistance — expected: 0.3 - 100 Ω at 68°F (20°C). Failure: Resistance outside of the specified range indicates a faulty motor, requiring throttle body replacement.
• Scan Tool: Throttle Position Percentage (THROTTLE POS) — expected: 60% or more when the accelerator pedal is fully depressed.. Failure: A reading of less than 60% at wide-open throttle suggests a problem with the throttle body assembly, accelerator pedal sensor, or wiring.

Scan Tool Commands That Help

• Toyota Techstream: Data List > THROTTLE POS — Used to verify that the throttle position sensor within the throttle body assembly is reading the full range of motion correctly. This helps differentiate between a mechanical obstruction (carbon) and an electronic failure.
• Toyota Techstream: Utility > Reset Memory — This function should be used after cleaning or replacing the throttle body to clear the old learned idle values from the ECM. This is a critical step before performing the manual idle relearn procedure.

Wiring & Ground Locations

• ECM (Engine Control Module) — Located on the driver's side of the engine bay, next to the main fuse box.. The ECM is the control center for the Electronic Throttle Control System (ETCS). All sensor inputs and motor control signals for the throttle body originate from or are processed by the ECM. A poor connection or rare internal fault can cause P0505.
• Engine Ground Points (General) — Key grounds for the 2AZ-FE are typically found on the left side of the cylinder head and the intake side of the cylinder block. A main body ground is also critical, often from the negative battery terminal to the chassis nearby.. Improper or corroded grounds can cause erratic behavior in electronic components, including the throttle body and its sensors, leading to incorrect readings and control issues that can trigger a P0505 code.

Real Owner Repair Stories

• CarKiller Forum User (2014 Scion xB, Automatic, 166k miles) — Rough idle with check engine light and code P0505.
  ❌ Tried (didn't work) Replaced spark plugs, Replaced throttle body, Replaced vapor purge canister, Smoke test (no vacuum leaks found), Verified fuel trim, PCV system, spark, and accelerator pedal signal were all good, Performed ECM memory clear and factory relearn procedure
  ✅ What actually fixed it After extensive professional diagnosis where all other components and systems checked out, the final step in the diagnostic tree was to replace the Engine Control Module (PCM/ECM). The shop noted that while this was the last possible cause, they could not guarantee it would be the fix, highlighting the extreme rarity of ECM failure.
• ScionLife Forum User (2008 Scion xB) — Vibration at idle while in drive (no codes initially), then P0505 appeared after replacing the throttle body.
  ❌ Tried (didn't work) Cleaning the original throttle body, Cleaning the MAF sensor
  ✅ What actually fixed it The user replaced the original throttle body to solve a vibration issue, which was successful. However, the new throttle body immediately triggered the P0505 code, even though the car ran perfectly. This case illustrates that a faulty replacement part or an incomplete idle relearn procedure can be the direct cause of the code, even when no actual idle performance issue is noticeable.

"I Checked Everything" — The Actual Cause

• In a documented case for a 2014 Scion xB, the vehicle passed a smoke test, ruling out vacuum leaks. Technicians also confirmed good fuel trim, a functional PCV system, and correct signals from the accelerator pedal. Despite replacing the throttle body and performing a factory relearn, the P0505 code persisted. The root cause was suspected to be an internal failure of the Engine Control Module (ECM), as it was the only remaining possibility in the official diagnostic flowchart.

OEM Part Supersession History

• 22030-28070, 22030-28071, 22030-0H030 → 22030-0H031 — Standard part revision and consolidation by the manufacturer.
  Heads up: The superseded parts are interchangeable with the newest part number.

Model Year Variations Within This Range

• 2008 (Post-revision): Toyota made a minor revision to the 2AZ-FE engine starting in the 2008 model year. The compression ratio was increased from 9.6:1 to 9.8:1, and the intake cam was revised for slightly improved power and torque. This does not significantly affect the diagnosis of P0505 but is a known running change.

Diagnostic Flowchart

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used OEM throttle body from a reputable salvage yard or a crashed vehicle can be a cost-effective alternative to a new aftermarket part, especially if the failure is confirmed to be the internal motor and not just carbon buildup. Given the high cost of a new OEM unit, a used one is a reasonable gamble.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Check for physical damage to the housing and electrical connector.
• Ensure the butterfly valve moves smoothly by hand (if possible) without excessive sticking or roughness.
• Ask for the VIN of the donor car to verify it's from a compatible year range and not from a vehicle with flood or fire damage.
• Prefer parts from JDM importers, as they often have lower mileage than US domestic equivalents.

OEM-only on this vehicle (don't cheap out):

• Engine Control Module (ECM) - Due to the need for VIN programming and the high potential for incompatibility, a used ECM is a significant risk and should only be sourced and programmed by a specialist.

Aftermarket brands forum-validated for this vehicle:

• Aisin (This is the Original Equipment Manufacturer)
• Hitachi
• Dorman (Specifically their OE FIX models which claim improved sealing against contamination)

Brands owners have reported issues with on this vehicle:

• Unbranded, no-name parts from online marketplaces can be poorly calibrated and may fail prematurely or cause codes to appear, as seen in some forum posts where new parts trigger codes.

Related OBD-II Codes

• P0171 — System Too Lean (Bank 1). Often appears with P0505 when the root cause is a vacuum leak, which allows unmetered air to enter the intake manifold, disrupting both the air-fuel ratio and idle stability.
• P2111 — Throttle Actuator Control System - Stuck Open. Can be triggered alongside P0505 if the heavy carbon buildup, common on the 2AZ-FE, physically prevents the throttle plate from closing to the commanded idle position.
• P2112 — Throttle Actuator Control System - Stuck Closed. This code may be set if the throttle body's internal motor is failing or if carbon buildup restricts the plate from opening correctly, leading to stalling and idle control faults.
• P2119 — Throttle Actuator Control Throttle Body Range/Performance. A general performance code for the electronic throttle body. It can be set with P0505 if the ECM detects that the throttle plate's actual position does not match the desired position for idle control, often due to dirt or a failing motor.
• P0300 — Random/Multiple Cylinder Misfire Detected. The erratic, rough, or surging idle caused by a dirty throttle body or a significant vacuum leak can lead to unstable combustion and trigger misfire codes.

Frequently Asked Questions