2003 s2k. idle bounces when engine is cold or warm, wont maintain steady rpm in lower rpm band (2-4krpm) under partial throttle. excelerates fine and will hold steady rpm high in rpm band (4k up). tried the map whack and resetting ecu but couldnt get the car to hold steady rpm while letting ecu to relearn the its maps.
any ideas? and how and where do you jump the diagnostic connector to check for codes

its my sis's car

 

The car is OBD2 you don't need to jump anything just hook up a reader. Have you tried cleaning yout IAC?

 

vacuum leak. spray some carb clean around the engine area and see if the idle settles out. when you find that area, look for the vacuum leak in that area.

 

Check the coolant level in the radiator. Low coolant will cause a surging idle via the IAC valve.

If the radiator is full, check the IAC valve itself, which may be clogged or stuck.