20V alve surging on light load

[Richard J Lebens <rick-l@rocketmail.com>]

1991 Audi 90 Quattro 20 Valve
I have been experiencing surging under light load in 2nd or 3rd gear
under light throttle.  While cruising it feels like the engine is
cutting out momentarily, kind of like when the AC is on (which it
isn't).  I replaced the oxygen sensor and now I no longer have a
hunting idle after coming to a stop but the surging is still there. 
The idle also isn't as smooth as it was a couple weeks ago.  I searched
for vacuum leaks with propane and found nothing.  Anybody got any
ideas?

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