I have a 2005 Honda civic. It is bucking while driving. Usually any where from 25mph and up. I brought it to a mechanic who gave it a tune up including changing the spark plugs. Still happening. Any ideas?

 

It could be a vacuum leak. Check all vacuum hoses for cracks or disconnections. If all else fails, take it to a shop that does real troubleshooting. The shop that tuned up your car should've never given you back your car before testing it. However, you might want to give them one more chance if they would further analyze at no additional cost to you.

 

does it do this when you mash the gas pedal to the floor?

is the check engine light on? if so does it flash?

if no codes, an no bucking while mashing the pedal,
you may have egr valve that is opening to much, causing this.
disconnect it and redrive the car, if the bucking is gone, replace the egr valve.