[Vwdiesel] Strange "power surge"

[jon]

A strange thing has been happening the past couple of months (started
before the well-known San Fran. trip, so it has nothing to do with that
debacle):

At low (just above idle) to medium low throttle, there is a power surge.
Then, when above that, everything returns to normal. It doesn't really
cause any problems, it's just not right. It's almost like the oppostite of
a slipping clutch, if you know what I mean.

Just before going to SF, when I first noticed this, I fixed a leak on the
injection pump. It was leaking out of the round spring cover (I forget
what it really is called). So, I pulled it off, stole a gasket from
another IP pump, and put it back together. I pulled the spring out, and am
not sure if I put it back in the same direction, if that even matters.

Could this spring be the cause, IP gurus?

BTW, this is a standard 1.6NA IP pump on a 1.9NA overland engine. Yes, I
know there are several variations of this pump, so if folks really want to
know, I can look at the number on the IP.
Thanks,

Jon