Engine missing under power

[Anthony Attard <ACA@nrc.gov>]

Hi everyone, I have a question regarding a problem with my  89 Audi-90Q.  In the
last couple of days, it has developed a "mis" in the engine under power only.   It
idles well.  I intend to check the plugs/ rotor button/distributor cap.  etc.,etc.   Also,
I noticed that a hose (vacuum hose ??)  located about the center of the engine
block, on the driver's side,  comes out the engine and  bends towards the back of
the cylinder head and connects to a steel pipe.  This hose is perished and has a
hole in it.  The question is, if this hose is leaking,  will it cause the engine to "mis"
under load??   Also, how do you determine if the Catalytic convertor is bad?? 
Unfortunately I do not have a manual.  

  Your help is greatly appreciated.  Thanks very much.

Tony .   89 Audi model 90/Q