Matt,
An exhaust system change from the original size to 3 inch seems unlikely to
decrease the vacuum supply enough to cause cruise control problems. The
vacuum reservoir (as long as it will hold 10 inches of vacuum) should
provide enough force to operate the throttle actuator while even when
manifold vacuum drops such as when climbing a grade.
The situation I outlined occurs only when there is a surge in speed up and
down immediately after the set button is pressed. Surges in speed during
steady state running may be caused by vacuum leaks from the reservoir, loose
or slack actuator cable, defective throttle actuator, or defective rear
wheel speed sensor. If you have ever noticed flutter in the speedometer,
that could indicate speed sensor problems. The speed sensor feeds the
anti-lock brake computer, and from there to the Powertrain Control Module.
The module supplies the speedometer and the cruise control with speed info.
Posting the page is a little tough, the book is two inches thick and I don't
have a scanner (maybe someday :-). If you have access to the book, it's
section 8H. If not, I can paraphrase the last paragraph about "unlearning"
the overshoot/undershoot in another post.
Neil
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