Possible Vacum Leak
 

I have a 1991 Cutlass Supreme. I have been hearing a whistling, hyming type sound from under the hood which has gotten louder with time. It seems the idol is off and car feels sort of sluggish. I have been told it is a vacum leak. I could not see it from standing over the engine. What is my next step?:rolleyes:

Get a can of carb cleaner and spray it in the area of the noise. If the idle picks up you found the leak. You can isolate it that way.

Thank you. The sound appears to be coming from under the iron slab-like piece on the top of the engine. It has 3.1 engraved in it. Does that have to come off to get to the leak?

That I can't tell you as I'm not intimately familiar with that engine.