1996 Idle increase/decrease with possible hissing noise!

[ortred]

My wife and I just bought a 1996 Ford Explorer with 62K miles on it. I have never had a Ford before and do not know if what I am hearing under the hood is normal or not. When the vehicle is in park and idling, the idle speed seems to fluctuate, (almost sounds as if someone were shifting the vehicle from park to drive, park to drive, etc.). When the fluctuation occurs there is a click coming from the air conditioning pump; the front portion of the pulley that is attached to the A/C pump stops rotating, even though the pulley is being driven by the belt; when that front portion of the pulley starts rotating again, that is when the click is heard and the idle speed fluctuates. Also, when you have the hood up and the vehicle is idling, you can hear a constant high pitch hiss, (kind of sounds like a gas turban engine!). The vehicle is a 1996 4X4 V6 4.0L; sure hope someone out there can tell me if this is abnormal or just the nature of the beast.

Thanks all,
Jason

 

[Hartman]

What you have might be a vac leak. I have the same hissing sound and clicking as you, but I haven't found the leak yet.