This will normally be a vacuum leak, you will have to get a mechanic to go over the induction and brake booster and check for a leak, start there.
mark (mhpautos)
Feb 28, 2010 at 9:04 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.