Bob---an "idle" speed of 2200 rpm between shifts or when it's supposed
to be idling, is more than you can adjust for with the vacuum retard
cannister on the distributor, or the tube that interrupts it, when the
coolant gets too hot. I have no practical experience with the EGR
system, so I can't comment to its effect on idle speed.
I would first go to what could cause this much of an increase. The most
obvious is the throttle linkage is in a bind, and could be looked at be
working by hand. (A temporary increase in the return spring pull may
tell you something.)
Secondly, the carburetor temperature compensator(s) could cause this
much of an idle increase when they start to go bad. Since there's
supposed to be no adjustment on these, I'll just pass on when the ZS
manual says: Replace them.
It has to be something that lets in a large quantity of air, and
can pull in fuel at the same time, (so it won't stall the engine.) Open
throttle plate(s) or the temp compensators both fill these needs.
Dick T
'73
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