I have a 2000 Ranger with the 4,o motor and 4x4 auto with overdrive. When I oull into the garage, the engine starts to whine. I can make it go away by gunning the engine a bit (in park). I thought it was a power steering pump and was all ready to change it. Just to make sure, I tapped the pump with a rubber hammer but the sound continued. Then I tapped the alternator. The sound continued. Then I tapped the black plastic air intake that runds down the center of the engine and the noise stopped. Then I tapped it again, and the noise started, Tapped again and the noise stopped.
Now I'm scrathing my head. What could possible be whining that is associated with this black plastic tube? I tightened the bolts that hold it down and also tightened all the sensors and other things that attach to it, but the whine continues.
Any help would be greatly appreciated. Vince

Try changing the air filter, if it has not been replaced in the last 25,000 miles.

Plastic intake on the 4.0 is prone to leak vacuum. Most likely when you moved the tube you moved a rubber connection. PCV tube ends very common on fords to leak. All common vac leaks on a 4.0 can be temp related. Gunning the engine changes the pressure in the intake making leak come and go. You can pull the belt off and run the engine to eliminate possibility of a drive accesory making the noise but it sure sounds like a vac leak. If it's the SOHC 4.0 the upper intake is 2 parts. The orings that seal intake to metal lower intake can leak, rubber grommets on hold dowd bolts can leak, and plastic plenum can warp along with vac lines and elbows. A smoke machine can help find leak but sometimes it won't show up unles engine is running. PCV system is common to fail that way.

Also don't spray carb cleaner around looking for a vac leak unless you're prepared to call the fire dept. Have seen many many fires start this way. If you don't have access to a smoke machine use a propane can with a piece of hose to hunt for the leak. Much safer than spray aerosols.

Not the air filter. Brand new. Thanks

It does sound like a vacuum leak. I will check hoses et al. Plus I leanred from another Ranger owner it might be the Idle Air Control Valve. At least I know it is not the power steering pump which I was about to replace.

Thanks for your help.

Use Mobil 1 ATF in your power steering system and you will likely never have power steering-related problems.

The problem seems to have been the air idle control valve which is attached to the plastic tube that runs the length of the engine . Removed the part (two bolts and an electrical connector), and cleaned it with alcohol and silicone lubricant. Cleaned the seat and rubber gasket. Reinstalled and have not heard the noise since. Thanks to everyone for their help. Vince

The problem seems to have been the air idle control valve which is attached to the plastic tube that runs the length of the engine . Removed the part (two bolts and an electrical connector), and cleaned it with alcohol and silicone lubricant. Cleaned the seat and rubber gasket. Reinstalled and have not heard the noise since. Thanks to everyone for their help. Vince

Great! Self rescue!
Kudos for posting the fix for everyone to see. That could help a lot of others.
Thanks again, Vince!