2005 SATURN ION HIGH IDLE 1800 RPM CAN YOU HELP

start in the engine bay
look from air filter to throttle body for any air intake leaks

if it is supercharged listen to the supercharger bearings

then anything spinning at high rpm from the serp belt
could be a bearing water pump or idler pully

if internal only could be something caught in the air vents

Replace the air filter and IAC idler air control valve.

COULD BE TPS (RPM) SENSOR,CLEAN THROTTLE BODY.

The speed control sensor will cause that and it makes it so it will stay in second gear until you can get to repair shop. Check out youtube and put your problem and see if anyone fixed it

it sounds like the ignition crntrol module

The P0506 means "Idle Control System RPM Lower Than Expected"
Hope it can help you!
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Adjust your idle on the throttle body! Should be a set of two nuts on throttle cables

SUSPECT A VACUUM LEAK. LOOK FOR BOKEN HOSES AND AIR TUBES.

COULD BE MANY REASONS, START BY CHECKING FOR VACCUM LEAKS AND MAKE SURE IDLE AIR CONTROL VALVE IS WORKING AND THROTTLEBODY IS CLEAN,GOOD LUCK.

check for a vacuum leak