These symptoms are typical of a vacuum leak. Usually that is on the small vacuum hose going to the cruise control servo, but often that hose taps off the large hose feeding the power brake booster. If that's what you have, check that larger hose too for leaks and loose clamps. If everything looks okay, run a temporary vacuum hose straight from the intake manifold to the cruise control servo. (Cap any hose ends that are left open by doing that). If that solves the problem, suspect internal leakage inside the power brake booster.
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Saturday, June 13th, 2015 AT 6:03 PM