Did the Check Engine light come on? Have you had the ECU scanned for fault codes?
If there are no codes, try cleaning the inside of the the throttle body.
2006 GT Deluxe - 5MT - 12.52 @ 109.33
311rwhp 328rwtq with stage 1 bolt-ons
"If you want a 2.3 Ecoboost, get the Focus RS. If you want a Mustang, get the V8."