99 ford explorer hard to crank problem iac valve humming

I have been reading that boards and still advise, as mentioned in the title i have an explorer that is almost impossible to crank cold, its not bad when its warm.. have cleaned everything possible and have read that replacing the iac valve would fix this problem but was told by a ford mech that it wouldn't, also was told that there was a hose that runs from the back of the upper plenium down to the lower intake that is stopped up or collapsed. but should the iac valve vibrate and hum, also the iac valve has the black knob on it, does that make my engine the sohc or the other one.. Any help would be appreciated.

The IAC valve supplies air when idling. As soon as your foot comes off the gas pedal, air is supplied via the IAC. That black cap is merely a air intake for the valve. If the IAC were bad you would have problems at all temps. It will hum because it has an electric motor in it. If you want to check it, unbolt it. look underneath into the ports. You'll see a plunger. Using a screwdriver try to move the plunger. it should move freely. I'v even held it motor side up and poured oil through the top port. It will drain through the bottom port. Usually cleans out any debris that may be holding it back.
To check the motor, take a resistance reading across the two prongs of the plug on the IAC side. Should read 10,000 ohms or better. Take a resistance reading from 1 prong to the case and then the other prong and case. You should'nt see any reading. Infinite resistance.
Again I don't think this is your problem but if it puts your mind at ease, you can move on. Hope this helped.

Thanks for the help, I found out that i had a bad lower intake manifold gasket allowing water to seep into 5 of the 6 cylinders,, fixed it and its all good now DOO!!!