97' ranger vacuum leak???

I have a 97 ranger that has check engine light on,,can't remember the code number the mechanic told me,but was something to do with emissions,his first "fix" was replacing the EGR valve,it was rusted in to,few days later light is on again,,,the whole time I've had this problem,,there is a "whistle" at about half throttle under a slight load,that increases with the throttle,then goes away shortly after 1/2 way,he has since went all over the engine trying to find a vacuum leak and can't,sounds to be coming from under the hood,maybe about midways on the firewall,doesn't do it at idle,so kinda hard to tell,,just wondering if anyone has ever experienced this? Also recently ABS light came on,,not sure if this is related or not,,but info is appreciated!!

Without a trouble code to go by you will be lost. The emmissions system contains the egr valve, dpfe sensor, vac lines, pcv, charcoal can, purge valve, sensor, gas cap and more. Get the right code and post it chances are if it is emissions related someone else is having the same or had the same problem..joe

will do,it's going back in the shop Fri. to pull the trouble codes again,,I'll post as soon as we see what it is,,Thanks!!