[Laird Scooby]

I wouldn't say it's conclusive James but could well be a symptom. Usually i've just sprayed carb and air intake cleaner into the valve and let it soak. Not having had a B230 with one on and on the B280E it's above the manifold/throttle body, i've just disconnected the inlet hose from it, given it a good squirt, cleaned a few other bits like the stubs on the inlet manifold for the various vacuum connections etc, started the car and then given it another squirt while running.

Also cleaned the throttle body in a similar way but that's the useful thing about the cars i've owned, they've always been easy access for things like that.