What idle valve line? These Diesels don't have any air throttle. The line from the manifold goes through a switchover valve then to the ALDA. It splits before the ALDA to provide a signal to the transmission vacuum amplifier (BFS). Which line is clogged?

Here, I found a diagram - http://www.peachparts.com/shopforum/2006956-post69.html

Here's one suitable for framing - http://www.peachparts.com/shopforum/2230146-post83.html

Sixto
87 300D