I just bought a 1991 camaro rs 305 TBI, when the car is at idle and in PARK you cant hear it but once you put it in drive or reverse at idle it makes a loud hissing noise, also if im in drive going down the road it will make that same loud hissing noise when I hit the throttle but if I let off the throttle and coast it stops making the noise. does anyome has any idea wht this could be? it sounds like it coming from the left side of the engine if your standing infront of the car near the left valve cover. anybody have this same problem?

 

Open element air cleaner? Odds are it is the IAC bypassing air around the throttle blades. Can't really hear it with the stock air cleaner.

RBob.

 

its stock air cleaner not open element.. ill check the IAC tho. the tube that runs from the valve cover to the air cleaner is loose on the valve cover.. also what is that tube called?

 

It might be your PCV valve line. There should be a largish tube (about the size of the brake booster vacuum line) that runs to the valve cover with a little device on the end that rattles if you shake it. That has your PCV valve (positive crankcase ventilation valve).

 

The hose with the PCV valve in it wouldn't go to the air cleaner. It would go to a manifold vacuum source, probably on the TBI unit.

The hose going from valve cover to air cleaner is the fresh-air inlet to the crankcase, the "other end" of the PCV system.

 

Both of those tubes fit into a rubber grommet that fits tight into the valve covers. Are those still there?