I'm going through my 86 N/A S4 because I need to smog it and it has a rough idle.

I ran into the fact that there is supposed to be a restrictor, or pill, in the vacuum line from the engine block the boost sensor. I measured 20" hg so I know I'm getting boost vacuum on the line. (and it points to not having a vacuum leak, although I could have an air leak somewhere else)

What is the impact if I don't have this restrictor?. .. . .Maybe a better question is if I need it, where do I get it?. . .Do I make it? . . .Does .050" diameter by .25" long sound good?

 

I do not run a restrictor in the vacuum line from manifold to boost control solenoid. Just run standard hose size. I don’t think worrying about this is your problem with rough idle.


Long story, (turbo) I’ve seen variations in boost response coming from boost gauge hose if running too large of diameter (vacuum hose from manifold inside a larger vacuum hose which connected to the gauge) but effects were minimal and have been corrected by running same hose ID as original ID hose, even another 3 feet longer.