Engine speeds up randomly at any speed over 40 MPH?

Hi,

The IAC can cause both. Oftentimes, the idle speed will vary up and down. Chances are the person that to you is correct.

As far as the IAC is concerned, take a look through this link. It explains how it works.

https://www.2carpros.com/articles/how-a-idle-air-control-valve-works

Also, here is a link that explains in general how one is replaced:

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

The IAC is located on the top LH Side Of the engine, in front of the Air Intake Assembly. See pic below

I hope this helps you. Let me know if you have other questions.

Take care,

Joe

See pic below.