An egr valve problem can be diagnosed in two stages.

I. Disconnect and plug the vacuum line to the egr valve. If the problem disappears, then you may have a vacuum problem.

II. I prefer to block off the egr passage with a piece of sheet steel. If the problem disappears, then the egr valve is somehow stuck open -- probably with deposits on the poppet valve. The egr valve would need to be replaced. Or again, there is a problem with the vacauum.

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95 E320 Cabriolet, 169K