[s-cars] Partial Throttle Surging

[mlp]

Has anyone on the list experienced, as best I can describe it, "partial
throttle surges or surging" under certain boost conditions?

The condition seems to arise & can be duplicated or created with a long
steady pull under load, like you can get on a long steady climb, by allowing
the car to accelerate in an upper gear, say 5th or 6th, while only slightly
opening the throttle just enough, say less than an 1/8th or so, that the
engine will make, and continue to slowly build boost without cracking the
throttle open any further.

In my car I when boost gets to @ 12 psi (a number suspiciously close many
waste gates  reputed "default" base spring pressure), then will begin an
increasingly aggressive swing, pulse between 12 / 18+psi as seen on,
reputably reliable, digital boost gauge.  By "aggressive" I mean one will
see almost instantaneous pressure swings from the base 11 to 12 up to 18~20,
13, 14, 15 & 16 etc. don't get to play much if any part in the natural
progression of events.

One theory that's been tossed out for kicking about, is that there is a
pressure difference across the throttle body plate, creating a pulse between
the intake side (i.e. downstream) of the plate and the turbo compressor?
Perhaps exacerbated by the ECU taking its pressure reading from the intake
manifold, which is upstream (on the other side) of the throttle plate.

Any thoughts, theories etc.?

Please Paul, no "choking the chicken" jokes.  I mean I think I may finally
have at least one car back!

mlp