There's also a flap in the crossover pipe; together the flaps 'tune' the apparent length of the intake manifold, as others have already noted. A third flap, just in front of the EGR valve, is designed to reduce the pressure in the intake manifold, thus sucking in more exhaust when the EGR valve is open. This "throttle" flap can be disconnected or even removed (two Phillips screws inside the intake pipe).

Note to 1996-97 W210 owners with the OM606NA engine: the throttle flap cannot be disconnected. The EGR electronics monitors the IM pressure and sets a code if the flap is not present and working.

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