I have checked and loosened the cables, yes.
If I gently let off the throttle (which I always do since I'm a good, smooth driver) the throttle will stay slightly open. 1100 rpm in neutral. If I stomp on and off again it will settle closed.
Can I increase three return spring pressure?

 

Have you tried cleaning the throttle plate and inside the throttle body? If it's dirty/carboned up that might be preventing it from closing fully.

 

X2 on the cleaning. I have bought a few used units and they were the same way until I clean them

 

yea, i thought that could be a potential issue. I'll try and tear it open soon

 

Sounds like the throttle stop gizmo is sticking partially open especially if the cable is returning OK and there some slack there.

 

X3 Clean the throttle plate! This is a common issue on ALL vehicles.

 

but when it is closed all the way, there is barely any spring tension on it. I feel as though I'd like to bend the spring to give it a new stop.

 

Are you thinking that maybe the spring is worn out? If so, it may be a better idea to replace it. You DON'T want that to break and cause a wreck!

 

IMO replace the whole unit as they can't be too expensive. You really don't need a throttle stuck open in an emergency situation ........... terrifying, I can vouch for that.