Fan Clutch
 

the fan on my 96 ranger 4x2 4.0L never goes off I have replaced both temp sensors and the thermostat what problems could the the fan always being on cause. when idleing my truck sometimes drops below 1000 rpms and sometimes even dies and sometimes when sitting at the red light the truck will act as if I am tapping the gas

Even a clutch fan will rotate when it is cold. It will just not rotate as strongly nor as fast. It will slip relative to the pulley, though you cannot see it. A good clutch fan will stop rotating immediately if you turn off the engine. I have heard that you can hear a clutch fan 'kick in' with a definite change in sound as it decides to lock up.
They last about 40k miles, and there is no 'absolute' test for wear-out.
If the engine doesn't idle properly, you may have other problems, such as ignition, plugs, wires or fuel injectors, pressure regulator, filter. Are there other symptoms? If the IAC will not kick up the idle when the A/C is engaged, it is suspect, and maybe should be cleaned or replaced.
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tom

well when the truck is at idle it will only idle down when the ac compressor stops spining while it is spinning the truck idles up alittle

how do you clean the iac i believe it is faily new but the guy drove on dirt road constantly