F2 is the setting for this and every time I set it both in FSX and FS9 in the settings it goes back to idle reverse.Does anyone know how to prevent this from happening please? I have battled with this for ages. :(

You need to move the repeat slider next to it all the way to the right to keep the key active in reverse. Otherwise once you release the key you have it assigned to, it will go back to idle.

In case you read my reply already I edited it while you may have been reading. I originally said to move the repeat slider to the middle setting.You need to move the repeat slider full right to get it to stay active when you hit F2. I had to open FSX to look at it myself.