Low idle - no power 2004 Ford Escape XLT

I have been experiencing a problem with sluggish acceleration as well as a low idle and a lack of power. Then while I was driving there came a hissing noise as if air was escaping from somewhere and the car struggled to reach 25 mph. I then had the EGR valve replaced and the hissing noise is gone and the acceleration is better but not what it should be and it still idles low. The mechanic said he didn't notice anything else that needed to be fixed. Any ideas as to where we should be looking? My car is a 2004 Ford Escape XLT.