What fell off My engine?

'86 328, My idle speed went to 1500 rpm. Visual inspection found a threaded hole in intake runner that leads to cylinder #4 in the front bank. Was it just a bolt or did I lose something else? I haven't had much time to get to know the car yet so I'm not sure what was there. I have a bolt in it for now and it has led to some interesting idle speeds so apparently whatever was there was leaking air before and somebody adjusted the idle with screw at the TBI instead of the idle adjust knob. Did I lose a vacuum fitting and line? Thanks for the help

 

hmmmm. Brakes still feel good but I'll check that.

 

Nobody have any ideas yet?

 

O.K. so I can find no evidence that the missing bolt was for anything but the bracket that holds the fuel lines. I put a new bolt in and the idle went down but now its all over the place. Its high after a run on the highway, then after 2-3 mins it drops down and pulses from 400-1000 rpm until it stalls altogether. On cold start it idles at 1100 and is rough and smells gassy.I can't locate any more vacuum leaks so My WAG is that whatever bolt fell out was the wrong size anyway and was leaking some air. The idle mixture may have been adjusted during this time and now its way off? The car runs great anywhere but idle, I drove from Cincy to Chicago last night and managed 20 mpg @ 75 mph so it seems to be just an idle glitch. Now if I can just figure out where to start.

 

LOL So today the car ran flawlessly from start up to the idle speed when warm. The only thing I did was rotate the cold start injector because somebody put it in upside down and the plug was rubbing the hood. Apparently the car will do what She wants.