← Back to list

2000 Toyota Celica P0505 Code: How to Fix Engine Light Fluctuations and IAC Valve Issues

Model: 2000 Toyota Celica Fault Code: P0505 Posted: 2009-04-12 08:35

My 2000 Toyota Celica has a recurring engine light that turns on and off. The diagnostic code is P0500, which indicates an issue with the idle air control (IAC) system. I've already tried several common fixes: replacing the air filter, cleaning the mass airflow (MAF) sensor chamber and element, using electrical cleaner on all connectors, and cleaning the throttle body without removing it—using both a soft toothbrush and dedicated cleaner. Despite these efforts, the engine light returns consistently. I'm now wondering whether removing and thoroughly cleaning the IAC valve mounted on the throttle body would help—or if it's better to replace it entirely. The only source for the required gasket appears to be the Toyota dealership. Could a vacuum leak also be causing this? If so, how can I identify potential leak points? Additionally, could a faulty PCV (positive crankcase ventilation) valve contribute to the P0505 code? Any insights would be greatly appreciated. Thanks, Ken

Related fault codes

P0505

Comments (3)

Anonymous 2009-04-13 17:54

Did you fully open the throttle plate during cleaning? If it's clean and in good condition, the IAC valve is likely faulty. Cleaning alone rarely resolves the issue—replacement is often necessary.

Anonymous 2009-04-13 18:36

Thank you for your detailed post—it’s very helpful to see real-world troubleshooting steps. I did open and clean the throttle plate as thoroughly as possible. After restarting, the engine RPM was slightly higher, but by the next day, the check engine light returned with the same P0505 code. I contacted the dealership and ordered the IAC gasket (o-ring), which will arrive Wednesday. They mentioned they typically start with a cleaning attempt before replacing parts. What's the best method for cleaning an IAC valve? I've seen suggestions using pipe cleaners or purchasing a $10 kit from Sears. You previously noted that IAC valves are often defective and require replacement—does cleaning ever provide a lasting fix? Also, I found a link where someone purchased just the IAC motor for about $40. Is this a viable option? What exactly fails in these components? Thanks again, Ken.

Anonymous 2009-04-14 16:40

IAC valves can fail due to either electrical issues or carbon buildup. We generally avoid cleaning them because it's often only a temporary fix and may void warranties. However, you can try cleaning as a test—though the valve will likely still not function properly if internally damaged. Cleaning does not resolve structural or electronic failures.