I have a 66 f100 straight six 240 3 speed on the tree. It runs and drives alright but when it's idling and I'm not accelerating it vibrates a lot. I was just wondering if anyone new what this could be or how to fix it.

 

Could be several things. I'd start with the PCV valve. Look for a hose going into the valve cover. It's attached to the valve. You should be able to pull the whole valve, hose and all out. Shake the valve. If you can't hear it rattle, it's bad. I'm pretty sure a new PCV valve is less than ten bucks. Standard practice to replace it during a tune-up.