Hissing sound on a 350 Mercury Magnum

[captbro 0]

Have a 2005 298 SC with 350 Magnums. Replaced distributor cap on port engine now all of sudden it is making

a hissing noise. At idle no noise ut a soon as you give it a little throttle the hissing starts and gets louder like

air is being sucked in. Could it bee the Air Control Valve???

[The MOST 0]

It might be a good idea to recheck the work performed...as well as the entire engine compartment. Something may have been reinstalled incorrectly, pinched, stepped or moved and blocking air intake somewhere.

[change order 0]

Have a 2005 298 SC with 350 Magnums. Replaced distributor cap on port engine now all of sudden it is making

a hissing noise. At idle no noise ut a soon as you give it a little throttle the hissing starts and gets louder like

air is being sucked in. Could it bee the Air Control Valve???

 

I bought a 2003 298sc and had this noise with one engine. Tracked it down to a small foam "muffler" inside engine throttle body. Pull the cover and spark arrest off of the throttle body and look into the port that feeds the idle air control motor. Use the other engine to compare.