LHS help from a Chryco tech....

i worked as a dealer tech for 17 years,two problems that cause that where lower intake,the gasket would split causing a vacuum leak . some times if you spray carb. cleaner under the intake,below thermostat area of lower intake.some time though you have to just pull lower intake and look for carbon tracking from split gasket. the other problem was the egr valve . this also easy to test .the two tubes comeing off egr to top of intake,can be pluged by inserting a sheet metal plate between gasket & upper intake.if car run better,bad egr. pm me and let me know what you find