idle problems on sportage

my engine light is on and when ticking over it tries to stall for about 5 seconds then the rev counter comes bak up to tick over mode but yesterday was reving betwen 2 and 3 thousand revs on its own like i was reving it been told could be a crank sensor

any ideas

shaunny

have any codes for us???

since been told its the cat and box as its faulty its sending wrong signals to the ecu is this possible

Common issue with idle problem is Idle AIr COntrol valve. Easy to take out (2 screws) and clean with gas or carb cleaner.
www.geocities.com/lmp4203/kiasport/IAC.jpg