I'm trying to find out what the cap looking thing is above the low idle screw. What is it? What does it do? What does it connect to? Mine has a rubber hose off it and just drips fuel on to the ground.

 

It's a vent and there really shouldn't be fuel behind it.

It drains fuel if it manages to get past the fuel pin and into the AFC housing.

Here's the fix: https://www.dieseltruckresource.com/...el-pin-153154/

 

OK, this is a new truck. The guy did alot of engine work. I have dropped the idle down and that helped to shrink the puddle, is there anything else simple I can do till I find a mechanic to take it to?

 

Any ideas where I can get a new vent cap, all the fuel that has gone through this one has left it in real bad shape?

 

Other than changing the O ring around the pin I dont think much else will work.
Could try a fuel conditioner or 2stroke oil in hopes of softening the seal.

A new overflow boot will come in the reseal kit, about $14 for the kit on eBay.

 

look in the sticky, good article shows the fix.