Have a 86 150 5.0 engine. I am trying to find a vacuum leak. When I step on the gas while moving it starts to whistle. When I come to a stop with the truck in drive the idle drops but doesn't stall. If I rev the engine in park, no whistle. Any ideas where to look. Thanks Bill

 

Where's the whistle coming from?

 

Steve83, the whistle is coming fron the engine compartment. That is why I think it is a vacuum leak. I am not a mechanic, just a guess. When I am driving with my foot on the gas it whistles. If I take my foot off the gas it is quiet. Parked, I will not be able to get it to whistle. Don't know what could be the problem. Thank You

 

If you have an automatic, have an assistant set the E-brake, hold the regular brakes, put it in gear, and hold the throttle where it whistles. Then you can reach a 3' piece of garden hose (stethoscope) into the engine bay and track down the source.

 

86ford,
I have an '88 F150 302 that does the same exact thing (except for the idle drop). I have been trying to track down that whistle for a year now and haven't found any vacuum leaks. What I've noticed is that mine only whistles when the truck is moving and the throttle is partially open. I can't get it to whistle standing still and it doesn't whistle at idle or WOT. This led me to believe that it might be due to a particular combination of air intake volume (throttle position) and wind speed- i.e. how fast the truck is moving. If you find out anything else post it on this thread. That whistle is driving me crazy!!!