M119 EGR Clean Out

[Forrest]

My 1992 400E passed its recent CA smog test easily,
except for the EGR functional test, which passed, but just
barely. The tech applied vacuum to the EGR valve when
the engine was idling. Normally the engine should stumble/die,
but has to be passed if the idle decreases at all. Fortunately,
the idle speed decreased a little. . The tech mentioned that
the EGR would probably have to be "cleaned out" to pass smog
next time.

I've checked and cleaned the EGR valve, it operates
freely. But the idle speed still only decreases a little when
vacuum is applied to the EGR valve.

Is there a good/recommended way to clean out the EGR
passages on an M119? And what about the deposits that
are removed, is there any need to be concerned about where
they end up?

Thanks,
Forrest