car idles goovey

my freinds 89 civic si starts up fine when the motor gets warm it starts reving really high uncontrolably adn then the check engine light comes on sometimes stays at 3-4 grand untell u turn it off any one have any suggetions.

check the iacv (idle air control valve) it is located on top of the trottle body. make sure all vacuum lines are conected and no wires on the harness are kinked. that may be the problem.
What is the code the check engine light threw??