crank position sensor?
 

my truck runs good n i cant tell anythings wrong until i stop at a stoplight or let it idle for awhile then itll rev up to about 2000rpm for a second then itll go back to normal. someone told me it was my crank postion sensor. lookin for some input thanks

scan for codes?

Your crank sensor wont adjust idle all it does it tell the rpms, and where the position of the crank is for the fuel pump..

engine light isnt on but will it still show codes