Your 2021 Seltos idles smoothly when cold but develops a rough, hunting idle once it warms up. The P0507 code indicating high idle RPM helps point to the cause—the idle control system is struggling to maintain proper speed once the engine reaches operating temperature.
Why Warm Idle Is Different
Cold engines need higher idle speed for stability. As the engine warms, the computer gradually reduces idle RPM. If something is adding air or preventing proper throttle closure, the warm idle target can't be achieved, causing hunting and roughness.
What P0507 Indicates
The P0507 code means "Idle Control System RPM Higher Than Expected." The engine is idling faster than commanded, and the computer's attempts to compensate create the rough, unstable idle you feel.
Symptoms
- Rough or unstable idle when warm
- RPM fluctuating or hunting
- Idle higher than normal (over 800-900 RPM)
- May be worse in Drive than Park
- Check engine light with P0507
Common Causes
- Carbon-fouled throttle body - Deposits preventing full closure
- Vacuum leak - Unmetered air entering the intake
- Dirty MAF sensor - Incorrect readings affecting idle control
- PCV valve stuck open - Adding unmeasured air
- Throttle body fault - Electronic throttle not positioning correctly
Throttle Body Cleaning
Carbon buildup is the most common cause. The throttle plate edges accumulate deposits that prevent full closure. Cleaning often resolves P0507:
- Remove intake tube to access throttle body
- Spray throttle body cleaner on plate and bore
- Wipe clean (don't scrub aggressively)
- Reassemble and perform idle relearn
Idle Relearn
After cleaning, the computer needs to relearn idle parameters. Drive normally for 50 miles, or have a shop perform the relearn with a scan tool.
Repair Costs
- Throttle body cleaning: $100-$200 (DIY: $10)
- Vacuum leak repair: $100-$300
- MAF sensor cleaning: $50-$100
- Throttle body replacement: $400-$800