1998 and later diesels are now smogged in California. Earlier diesels are still exempt and are not inspected at all. For those living in places where older diesels must be smogged, it's probably best to leave the EGR valve and its plumbing on the engine and use a removeable defeat. The two easiest defeats are first, a BB in the vacuum line to the EGR valve. When the car goes to be smogged, remove the BB. Second, for later models where there's an electrical connection in the EGR valve, lack of vacuum causes an error in the EGR electronics. For these engines, a home-made solid gasket can be fabricated from sheet metal to replace the factory gasket between the EGR valve and the intake manifold. Now the EGR valve can open or close all it wants but the gasket prevents exhaust from getting sucked into your intake manifold. For smog testing just put the factory gasket back.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970