Changing the EGR valve is easy, it is just a few bolts. One problem I had on my HF was the tunnels in the IM were clogged with carbon. I managed to get this cleaned up with tiny shots of carb cleaner. If you apply vacuum to the EGR hose while the car is idling you should be able to see the diaphragm move and it should kill the engine at idle. If the diaphragm moves and the engine doesn't die, you probably have a clogged IM.