Try cleaning your maf and map sensors (not sure this will fix it but worth a shot, pretty easy to do). Then I recommend scanning with a code scanner, also try to look for vacuum leaks. Try doing a relearn procedure for the throttle How to: Perform the Throttle Relearn Procedure on a 8th gen 2006 Honda Civic Si 2.0L k20z3 ivtech - YouTube. To me it seems like it will have to be something throttle body or throttle plate related. It is very possible that the mechanics didn't do the correct throttle relearn procedure (the link I have up there is to do it manually, which doesn't always work), which is when you take a programming obd2 scanner/reader and use the function throttle relearn procedure in it. It could also be a vacuum leak like I said. Or your throttle pedal could be sticking, I personally hate the drive by wire in our cars.