Thanks for the replies.
After a few frustrating days of trying to repair this issue I finally figured it out. The issue was a silly one.
I did a flight from my local airport to another airport in my area. This is a flight I’ve done many times in real life. Once I got to my destination I taxied to the run up area and decided to come back another day to finish the return flight. What I discovered is that something must have been corrupt with the save file. After a couple of days of loading that file and trying everything to repair the throttle issue I decided to start the flight over again from my home airport.
What I found was if I started fresh without loading up that saved file the throttle worked perfectly.
Go figure!