1994 Explorer stalling when idle

Help! A couple of days ago, my 1994 Ford Explorer started stalling when the engine is idle, for no apparent reason. When idling, the engine will now start to shudder and then die. All electrical systems seem to be functioning normally. There's also an additional concern of a hissing noise when I touch the accelerator. BTW, the mileage is 147,000.

IAC Valve?