What do you think happened?

We drove the car to the last car show of the year and when we got there it was idling ~about 3000 RPM. It's been fine all summer and I haven't touched it. I have to back off the throttle cable adjustment almost a half inch to settle it down to normal. How on earth did I lose almost a half inch of adjustment? Still scratching my head on this.

1974 Dodge Dart Swinger with a 360 LA and Holley 750 DP. Nothing crazy about the set up. Lokar throttle cable and kickdown. Been in place for over 3 years.