Fast or runaway idle
 

We have 2012 Hyundai Accent from time to time regardless of the weather the car will race up to 1500 - 2000 RPM with the foot of the gas pedal - its like the throttle cable is stuck but this car does not have a cable. The dealer is no help, it has to act up for them to fix it, a local mechanic scanned the computer and did not see any codes - any suggestions ?

Clean IAC (idle air control), EGR (if it has one), MAF (if it isn't a MAP)

A stuck idle air control valve. These are cheap. It's not hard to change it. (located on the intake throttle body, held in place with 2 small bolts)
Cleaning it may not really fix it...
These things get gummed up, and they stick. I bought one on Amazon for like $14.

Yeah...I know what you are saying. It might be better to get some tools and fix your own car.