P0506: OBD-II code P0506 means the engine is idling lower than the PCM commanded — usually a dirty throttle body or a vacuum restriction.

Symptoms

• Check engine light is on; idle speed sits below the normal 700-900 RPM range for the engine.
• The engine may stumble at stops, threaten to stall, or actually stall when coming to rest.
• Rough idle and slow return to idle after throttle release.

Common causes

• A carbon-clogged throttle body restricting the idle bypass air path around the throttle plate.
• A failed idle air control valve stuck partially closed on cable-throttle engines.
• An engine mechanical issue (low compression, PCV problems, or a large intake restriction) reducing available idle air.

What to do?

Clean the throttle body and (if separate) the IAC valve. Perform a throttle relearn with a scan tool on drive-by-wire engines. Check for large intake restrictions or PCV issues. Replace the IAC valve if cleaning doesn't restore idle speed.