OK try this if you can get your hands on a propane torch. Take the torch but DONT light it just let the propane flow out and while the car is on manuever it between the intake manifold and the head and run the unlite torch along the gasket. If there is a gasket leak then it will idle higher if not then nothing should happen. I have the same problem you have. A leak between the head and the manifold could be the problem.