93 z28 revs low when stopped

chances are it is a vacume leak. thats the most common problem on a fuel injected car. you can take a propane torch and follow vacume lines with it. *dont light the torch just let the propane come out* and if you pass over a leak the cars idle will change then just change the hose and you are set.

if it was a vacuum leak the idle would be high

Yes vacuum leak would cause high idel. On gm cars of that age there is two common and easy to fix problems. First inspect the throttle body( take the rubber intake boot off) If its all dirty clean it with some intake or carb cleaner, These get restricted with crud and dont let the car breath right. Also on the side of the throttle body there is an idel air moter. Same idea , take out the two torx screws and clean it out and the passage it sit in, same idea cruds up. The second is the mass air senser in the intake pipe. Be very gentle with it and again, clean it out inside with a q tip, very gentle the little wire inside is fragile. This tell the computer how much air is entering the engine so the computer can give the right amount of fuel and spark timing

thanks a lot. thats a great help. ill give it a try

im havin the same problem ! i used carb doctor for injrction set, n' wd-40 for electrical plugs all is good now