P0505
Fix within a few daysYour engine's computer isn't able to control the engine's idle speed correctly.
Code P0505 means your engine's idle speed control system is malfunctioning. Common causes: Faulty IAC valve (60%), vacuum leaks (20%), dirty throttle body (10%). Drivability: Limit driving, fix within a few days. Repair cost: $50-$220 DIY, $150-$500 professional.
Can I Drive With P0505?
Limit driving, fix within a few days
Essential trips under 10 miles, avoid highways and heavy traffic where stalling would be dangerous.
Stop driving immediately if: Frequent stalling, engine dying at speed, or inability to maintain any idle.
Symptoms of P0505
- 1Engine idles rough or erratically
- 2Engine stalls when coming to a stop or at low speeds
- 3Engine idles too high or too low
- 4Engine dies immediately after starting
Common Causes of P0505
Parts most likely causing this code, ranked by probability
The IAC valve regulates the amount of air bypassing the throttle plate to control idle speed, and if it's dirty or faulty, the computer loses control.
60% of P0505 cases are fixed by replacing this part
Unmetered air entering the engine through a leak confuses the computer, making it unable to maintain a stable idle.
20% of P0505 cases are fixed by repairing vacuum leaks
Excessive carbon buildup around the throttle plate or in the IAC passages restricts airflow, preventing proper idle control.
10% of P0505 cases are fixed by cleaning the throttle body
Damaged wires or a corroded connector prevent the computer from sending proper signals to the IAC valve.
5% of P0505 cases are fixed by repairing wiring or connectors
A faulty computer can fail to properly command the IAC system, leading to idle issues.
5% of P0505 cases are fixed by replacing the ECM/PCM
Check These First (Before Buying Parts)
- Visually inspect the IAC valve and its electrical connector for any obvious damage or loose connections.
- Spray throttle body cleaner into the IAC valve opening and around the throttle plate to remove carbon buildup.
How to Diagnose P0505
- 1Visually inspect the IAC valve and its electrical connector for damage or corrosion.
- 2Remove and clean the IAC valve and the throttle body bore with throttle body cleaner.
- 3Check for vacuum leaks using a smoke machine or by listening for hissing sounds around vacuum lines and intake manifold.
- 4Test the IAC valve's electrical resistance and operation using a multimeter or scan tool (if applicable).
- 5Inspect the wiring harness leading to the IAC valve for continuity and shorts.
P0505 on Popular Vehicles
Honda Civic
1996-2005P0505 on these models is very commonly due to a clogged or faulty IAC valve. Cleaning the valve and throttle body is the first step, but replacement is often needed.
75% fixed by cleaning or replacing IAC valve
Toyota Camry
1992-2001Similar to Honda, older Camry models are prone to IAC valve issues. Carbon buildup in the throttle body and IAC passages is a frequent culprit.
70% fixed by cleaning or replacing IAC valve
Ford F-150
1997-2003P0505 on these trucks often points to a failing IAC valve. Vacuum leaks from aged hoses or intake manifold gaskets are also a significant factor.
65% fixed by replacing IAC valve or repairing vacuum leaks
Frequently Asked Questions
What does P0505 mean?
P0505 indicates that your vehicle's engine control module (ECM) is unable to effectively control the engine's idle speed, leading to unstable or incorrect RPMs when the vehicle is not moving.
Can I drive with P0505?
Limit driving, fix within a few days. Driving with P0505 can cause your engine to stall unexpectedly, especially when stopping or at low speeds, which creates a safety hazard. Get it checked out quickly.
Will P0505 clear itself?
No, P0505 will not clear itself. The underlying issue causing the idle control malfunction needs to be diagnosed and repaired. The code will persist until the problem is resolved.
How do I fix P0505 myself?
Start by cleaning your idle air control (IAC) valve and throttle body. If that doesn't work, test the IAC valve for proper operation and resistance, and check for any vacuum leaks around the intake manifold and vacuum lines. Replacing a faulty IAC valve is a common DIY fix.
How much does it cost to fix P0505?
DIY repair costs for P0505 typically range from $50 to $220, mainly for an IAC valve or throttle body cleaner. Professional repair at a shop will cost between $150 and $500, including parts and labor.
P0505 keeps coming back - why?
If P0505 keeps returning, it means the root cause was not fully addressed. Common reasons include an overlooked vacuum leak, a faulty IAC valve that wasn't replaced, a dirty throttle body that needs more thorough cleaning, or a deeper electrical issue with the wiring or even the engine's computer.
Will P0505 fail emissions/smog test?
Yes, P0505 will cause your vehicle to fail an emissions or smog test. An unstable idle directly impacts exhaust gas composition and indicates a fault in the engine's emissions control system.
What's the difference between P0505 and P0507?
P0505 indicates a general malfunction in the idle air control system, meaning the computer cannot achieve the target idle speed. P0507 specifically means the engine idle speed is higher than expected, which is one possible symptom of a P0505 malfunction.
P0505 on Honda Civic?
P0505 is a common code on older Honda Civics (especially 1996-2005 models) and is almost always caused by a dirty or failing Idle Air Control (IAC) valve. Cleaning the IAC valve and throttle body often resolves the issue, but replacement of the IAC valve is frequently necessary.
Questions to Ask Your Mechanic
Did you test the Idle Air Control (IAC) valve's electrical resistance and operation?
Good answer: Yes, I checked the resistance and it was out of spec, or I saw it wasn't responding correctly to commands from the scan tool. I also checked its connector for corrosion.
Did you perform a smoke test to check for vacuum leaks?
Good answer: Yes, I smoke-tested the intake system and found a leak at the PCV hose (or intake manifold gasket, etc.) which I repaired.
Repair Cost Estimate
DIY Repair
Parts only
$50-$220
Shop Repair
Parts + labor
$150-$500
Save $100-$280 by doing it yourself
Difficulty
intermediate
Time
1-2 hours
Intermediate - requires some diagnostic steps beyond simple parts replacement, including testing and checking for leaks.
Cost of Waiting
Ignoring P0505 can lead to your engine stalling unexpectedly, which is dangerous in traffic. It also puts extra strain on your starter and battery from repeated attempts to restart the engine. A $100 IAC valve replacement now prevents potential safety hazards and wear on other components.
While You're In There...
If you remove the throttle body to clean it or access the IAC valve, replacing the gasket prevents potential vacuum leaks.
A clean air filter ensures proper airflow to the engine, which is critical for stable idle, and it's often accessed during this repair.
Tools You'll Need
- Socket set
- Screwdriver set
- Throttle body cleaner
- Multimeter (for testing IAC valve)
- Scan tool (optional, for live data and commanding IAC)
P0505 is a common idle control issue. Most repairs involve cleaning or replacing the IAC valve, which is a straightforward fix that will get your engine idling smoothly again.
- Family-owned since 1957
- 990,000+ happy customers
- Fast nationwide shipping
- Easy returns
Your Next Steps
Step 1: Clean the Idle Air Control (IAC) valve and the throttle body thoroughly with throttle body cleaner. Disconnect the battery for 15 minutes after cleaning to reset the computer's idle learning.
Step 2: If cleaning doesn't fix it, test the IAC valve's electrical resistance with a multimeter. If it's out of specification or doesn't respond to commands from a scan tool, replace the IAC valve.
Step 3: If the IAC valve tests good, perform a smoke test to find and repair any vacuum leaks. Parts you'll likely need: new IAC valve, throttle body cleaner, throttle body gasket, vacuum hoses.