P0505: Idle Control System
What Does P0505 Mean?
P0505 is a diagnostic trouble code indicating: Idle Control System. This code relates to the vehicle speed and idle control system. It has been reported in NHTSA complaints across 4 different vehicle models.
The vehicle speed and idle control systems manage engine operation at rest and in motion. The Vehicle Speed Sensor (VSS) provides real-time speed data used for fuel calculations, shift timing, cruise control, ABS, and speedometer display. The Idle Air Control (IAC) system regulates airflow to maintain target idle speed (typically 600-900 RPM). On electronic throttle control vehicles, the ECM uses the throttle body motor directly. When the ECM detects faults in these systems, drivability problems like stalling, surging, incorrect speedometer readings, and cruise control failure are common. Speed sensor failures are often caused by metal debris from internal transmission wear accumulating on the magnetic sensor tip. Idle problems are most commonly caused by carbon buildup in the throttle body restricting airflow.
Symptoms of P0505
- ⚠️ Check engine light on
- ⚠️ Erratic or inoperative speedometer
- ⚠️ Unstable idle — surging, hunting, or stalling
- ⚠️ Cruise control not working
- ⚠️ Transmission shift quality issues
- ⚠️ ABS or traction control warning light
Common Causes
- 🔍 Faulty vehicle speed sensor or idle control valve
- 🔍 Carbon buildup in throttle body
- 🔍 Vacuum leak affecting idle control
- 🔍 Wiring issue in sensor or actuator circuit
- 🔍 ECM or instrument cluster fault
P0505 Reports by Year
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"CHECK ENGINE LIGHT CAME ON AND THE PERFORMANCE OF THE VEHICLE IS BAD. BAD IDLE, WEAK ENGINE, JUST THE CAR IS NOT PERFORMING PROPERLY. I USED THE SCANNER TO SEE THE CODE AND I HAD MORE THAN ONE . P0171 P0505 P117B P0441 P0455 . FUEL/AIR MIXTURE IS LEAN . AND I HEAR THE FUEL PUMP MAKING THAT NOISE THA"
— Toyota Camry owner, 06/20/2020
"Sudden, unexpected, surprise Surging Idle upon placing the vehicle in Park after driving a 15 minute distance at a top speed of 35mph. Loud Surge up to 2.5 (x1000RPM) Sounds like the Engine Shifted Idle Drops down and immediately begins Surging up again. Idle is high while driving. Some chugging upo"
— Toyota Rav4 owner, 06/16/2025
"A couple of months ago, my car started running a little rough as it would sit in idle mode. When suddenly my check engine light came on. I checked the codes and they seemed to be P0445 Evaporitive emission system leak detected (large leak). And P0441 Evaporative emission system. Incorrect Purge Fl"
— Toyota Avalon owner, 10/10/2025
Source: NHTSA Complaints Database
Most Reported Vehicles for P0505
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | TOYOTA CAMRY | |
| 2 | TOYOTA RAV4 | |
| 3 | TOYOTA AVALON | |
| 4 | CHEVROLET MALIBU |
Diagnostic Tips
- For speed sensor codes: check if speedometer works — if not, output speed sensor is likely bad
- For idle codes: clean throttle body first — carbon buildup is #1 cause
- Check for vacuum leaks with smoke machine
- On electronic throttle vehicles, throttle body relearn may be required after cleaning
Common Mistakes to Avoid
- ❌ Replacing idle air control valve without cleaning throttle body
- ❌ Not performing throttle body relearn after cleaning
- ❌ Ignoring vacuum leaks as cause of idle problems
Frequently Asked Questions
Why does my car idle rough after cleaning throttle body?
Can a bad speed sensor cause transmission problems?
How much does a speed sensor cost?
What To Do Next
Possible Fixes
- 🔧 Replace vehicle speed sensor
- 🔧 Clean throttle body
- 🔧 Replace idle air control valve
- 🔧 Repair vacuum leak
- 🔧 Repair wiring/connector
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1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.