I had this happen this summer with a newish coil--about 8 months old--after it inexplicably died on the highway. We wound up replacing the coil (very weak spark) and it fired back up.

For what it's worth I replaced my O2 sensors this weekend with Delphis and do not have any of the idling / hissing issues anymore. However, the "old" NTK sensors were put on less than a year ago...

I can only guess that either pulling too much Seafoam too quickly through the intake manifold roasted the sensors, or simply moving around the 02 sensor wiring might have separated the loose ground in the harness. Like before, I sprayed the connections with electronic cleaner and put a healthy daub of dielectric grease on the fittings.

In the past year I too have replaced the PCM along with everything else (IAC, MAP, TPS, IAT, CPS, PCV, coolant temperature sensor, thermostatic fan clutch, emission canister sensor, vacuum hoses, fuel pump, injectors, plugs, wires, plenum, cylinder heads, valve cover gaskets, catalytic converter, throttle body, etc.) except for the gas cap.

Given that I frequently change out the oxygen sensors I'm really surprised that the idling issue seems fixed. I am going to stay away from Seafoam treatment and Lucas Fuel Injector cleaner and see where I stand in about 6 months.

Sorry to be so hard-headed about the 02 sensor swap; I was really skeptical that a part I had replaced multiple times was at fault. But it has cured my idling problems for now. I may have gained about 1 mpg (I cruise at 16.5 mpg at 65mph in the South Texas flatlands), but I will be looking for a spare 02 sensor harness next time I'm at my local junkyard.

Best of luck!