2000 mistubishi galant es idling rough seriously

Have you run an error check on vehicle. You can have this done for free at most auto parts stores. Almost sounds like the idle sensor is having issues, but can not be sure at this point. Make sure the choke isn't sticking or hanging up if carbureted.

if less than 600 then this could be your problem

NO, the on-board computer system will reset the IAC unit automatically, drive the car at over 20 mph for more then 2 min.

Code P0505 is a problem with the IAC (idle air control) which regulates the idle speed. To check it quickly, disconnect the IAC connection located below the throttle body near the firewall. Start the car and the idle should run around 1300 rpm at idle. If this is the case then the likely cause it a bad idle motor. The cost of a new one is $110 at Pep Boys or $30 at a Pick n Pull. Keep me posted, thx.

that means could be vacuum leak

You should have your TPS and EGR looked at as those cause rough idles...Other causes are bad idle air control valve, bad plugs, bad distributor cap & rotor, a bad wire, bad O2 sensor, etc...

the roughness at idle is the shocks .replace the shocks. i had the same problem

I would take a look at possiable damage to the PCM (powertrain control module)

car out of cruise control flutters or runs rough from 45 mph to 55 mph and once over 55 mph runs smooth. I notice from 45 to 55 the rpm guage moves with flutter or rough running engine. when i put in cruise control it smooths out.

Maybe just bad gas. Change fuel filter, Add some fuel conditioner to it, or fuel treatment,with moisture remover, and top it up with fresh fuel.