Problem with idle. idles low then cuts off

[stock 92 gt]

Title says it all...cant keep it going without pressing nthe gas. 91 mustang 5.0. hissing sound coming from around dist. peice of rubber...looks like a vaccuum cap. fell out from under the car. quick explanation please. how to fix?

 

[90mustangGT]

Bad vacuum leak, you already know. Now plug it and recheck.

 

[clarkjr]

If you can find the leak, hit the auto parts store and see if you can match up a cap to it.