I've checked that vacuum hose and it's fine. I can't tell exactly where the hissing is coming from because it only does it while I'm driving, not while revving it while stopped.

I checked vacuum and it's reading a steady 21 at idle, and 22 at higher rpm. It doesn't seem like a vacuum leak afterall.

It wont start at all when it's cold. After it gets above 40F or so it will start, but only if I hold the throttle to the floor. After it starts, it runs perfectly fine until it warms up, then it stutters and hesitates when accelerating from idle, not so much when accelerating at higher speeds.

If I unplug the AMM, the idle speed increases, but it stumbles and stutters much more when accelerating. If I unplug the O2 sensor, I can't tell much difference really, but the ECU seems to think the O2 is ok, and the readings I got from it checked out ok.

Thanks for your post. Please keep them coming. I'm out of ideas.