How do you tell if IAC is going bad if use- ing a scanner?

Question

How do you tell?

Answer 1

For the scanner to be of use, you must know what you are looking for, and different vehicles use different strategies for the IAC, and even within manufacturer make, different years will have different demands.
It is also important to know if you have access to a SCANNER or a CODE READER.
Many times they are referred to as the same thing, generically, but a scanner allows us to actually read values (known as P.I.D.'s) and in some cases actually control devices (bi-directional control). A code reader merely identifies a code, displays a code ID number, and it will allow you to clear some codes from some systems.

Answer 2

Depends on the make but most scantools will allow you to operate the IAC and some have their own 'test' mode for actuators. If there is no test mode, go all the way open and all the way closed. You should be able to do this while not running and when the engine. There will be very noticeable changes in RPM and the engine may even stall if the IAC works properly.