Check engine light on

I have never heard of such a fault code. Do you have the exact fault code number that I can look up?

High idle speed is almost always due to a vacuum leak. Fault codes typically indicate where to start looking for the cause of a problem. The description you listed is for the result of the problem. You already know the result is idle speed that is too high, so there is no point in having a code tell you that. That is why it is better to know the code number.

P0068 MAP/MAF - Throttle Position Correlation.
P0507 Idle Air Control System RPM Higher Than Expected.

Dandy. I can see how that second code got interpreted.

Code 68 is the one to concentrate on. Code 507 is just indicating the result of the problem. It will not be of any help with the diagnosis. There are two ways to approach this. The best way is with a scanner so you can view live data. Code 68 is saying engine speed is not consistent with how far the accelerator pedal is pushed, or when you have electronic throttle control, engine speed is not what is expected for how much the throttle blade is open. The scanner will let you see what the engine computer is seeing and responding to. The second approach, and to say this a different way, there is likely a vacuum leak.

Vacuum leaks cause engine speed to increase without a corresponding increase in power. The engine computer is seeing the throttle is closed, yet engine speed indicates the throttle is open. Start by pinching off various vacuum hoses to see if idle speed drops. Listen around intake manifold gaskets, or spray water or carburetor cleaner on the gaskets to see if idle speed is affected.

If you have the "throttle-by-wire" system, those have all kinds of safety measures built in and everything must be working properly, but you must understand there are a lot of ways the cruise control system can become inoperative. The engine computer can simply refuse to allow it to work when it detects some other problem. You can have an electrical problem as evidenced by the indicators on the instrument cluster you are used to seeing do not turn on. With the older systems that used the common sense throttle cables, the servos were run on engine vacuum, and a vacuum leak could make the servo not strong enough to pull the throttle cable.

You need a scanner to look at the long list of "Inputs/Outputs" related to the cruise control to see what does not look right. On my Chrysler DRB3 for older cars, it actually lists the "reason for last cutout" when you are looking for why the cruise control does not work or stopped working. You have to view that while on a test-drive, otherwise the reason listed will be "vehicle speed below minimum threshold", meaning you have to be going thirty to thirty five mph before it will engage. If you see "system turned off" even though you did not, you would know to look for an intermittent wiring or connector terminal problem. There are a half dozen other things it can list as reasons the system does not work, but it is up to you to figure out if they are related to some other problem.