87 300SDL heating question and rough idle
 

So,
on my 300SDL it only blows air up to defrost the windshield. No matter what i press it never blows down to warm the feet. Not sure what that could be.
Also when I put the car in Drive it will start to idle rough, when i shift it into neutral it idles fine. Not sure if the system is sucking in air or not. Had a fuel leak that I just fixed but that didnt solve the problem.

You need to replace the vac elements behind the glove box. $150, 30 minutes and off you go. I would verify there are no other leaks in the system and that the PBU is workingn properly, but chances are that is your problem I outlined earlier.

Check your motor mounts and trans mount, they cause vibration often if failed. Figure about $60 for all three and a few hours to install.