Plantman if you havn't done this already pull your crossover pipe and take a look inside. 330k miles is a long time to let the egr build up crap. Mine was pretty bad at 233k. My theory is that if the car is driven on the highway more and under constant boost the crap is driven deeper into the manifold. My runners were getting pluged up. I pulled off the vacum line and caped the fitting's. After I cleaned out the manifold I got a plate made that fit between the egr and manifold.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200