Let me first say I got these from toolman77 here on the forum as well as a in cab gun rack with flashlight clips. I have been very happy with both. If I could change anything I would get a bit sturdier mirror.
It kicks the pants out of auto heat and air. You can plow your driveway in long johns with the window down. AC is the same, you won’t run it wide open for long
Mines the same way it has a high idle detent. If you pull it farther it will spring back. I am thinking there is a spring somewhere that could just be removed so it will stay put.
As for the original poster, try replacing your battery if it is old, I noticed that these little diesels love a good amount of cca. Maybe try a cold start with some jumper cables hooked up to see if there is any difference.