I have a 1987 305 TPI. I am missing a big screw that holds together the plenum and the intake( very top piece of engine). Can this cause any problems? Or even vacuum leaks? My car is idling really really high and the throttle gets stuck open.

 

Missing a screw CAN cause a vacuum leak with a high idle, not only get a replacement screw but also check all screws to see if they are loose. Torque them per manual specs as you could strip them out. Also check the throttle body butterfly shaft for any slop. Leaks any where can cause a high idle problem.

 

Throttle body butterfly? Okay I just ask because my car is idling very high, and seems to just want to get away from me when im driving it. I will get this screw replaced and see if that helps at all.

 

Maybe i should have been more specific, I should have said, look for any slop in the throttle butterfly shaft, up, down, side to side. The bushings wear and cause slop which cause's air leaks, and sticky butterfly's. Remember too, you have one screw missing, you may have others that are loose.

 

Where should I be checking for air leaks? I am starting to think my problem is from a leaking vacuum

 

All around the plenum, runners, throttle body, intake, vacuum lines. With the car idling, Which you stated was a high idle, spray carb cleaner in the gasket area of all mating areas, and listen for an idle change, (be careful not to spray too much as it is flammable) Check all vacuum line for breaks and cracks. Did you replace the missing screw yet? And look for any others that are loose?