HISSING NOISE & CHECK ENGINE

On my 1998 Tacoma 2.7L 79780 miles, I started hearing an intermittent hissing noise, now check engine light is on. The engine runs and performs fine. Does anyone have any ideas or suggestions?

Check for a loose or cracked vacuum hose. Start on EGR system, then vapor recovery system, then PCV.

I have the same problem. I hear an intermittent hissing sound when I hit the gas. My check engine light came on a few months ago and then went off msteriously. I went out and bought a new PCV valve and i can't seem to find where it is to replace it. There is what looks like a pcv connected to a hose sticking out of the valve cover, but it is threaded into the engine. My friend told me that the hissing sound might be an exhaust manifold leak, my ride runs a little rough also.