1994 F150 Extened Cab 62K original miles. I hear what is obviously a vacuum noise when the truck is cold and outside temps are below 32 degrees. The noise is a loud whistling that stops once I raise the RPM. At idle it returns. Tried a spray bottle with water around the hoses in the engine compartment with no luck. Any ideas?

 

Try Carberator cleaner around the parts where you used the water instead. When / if you notice a change in the idle, that is your leak. Also try around the exhaust.

 

I've got the same problem with my '94. It sounds like a vacuum line is disconnected somewhere, but I can't find it.

 

Thanks, I will try carb cleaner. BTW the idle is not affected with or without the noise. The noise stops after things warm up. I suspect something is expanding and contracting with the temp. changes.