how much vaccum should a stock engine pull at idle? I was thinking 17 to 22 but I'm seeing 12 to 13 in my '94.

 

~20"Hg (= ~10"Hg MAP at sea level)

 

12 to 13 is a little low. you should see about 15-17

 

Sounds like it has a non stock cam.

 

My 93Z is around a constant 18 to 20"Hg at normal idle...

 

Depends on cam overlap- and maybe exhaust restriction, though I bet that isn't a factor here. Should be pretty high, assuming good mechanicals- gaskets, valves, etc. Can you adjust the timing? What RPM are you idling at?