My car just started to run perfect, now when im anywhere from 1500 rpm to 2000 my car sputters and bucks until i shift into the next gear. i drove like half a day after tuning my car up and then it just randomly started doing this,. if anyone has any info or can help it would be greatly appreciated, thanks.

 

Check the cap & rotor first.

 

Also check for vacuum leaks, but if you haven't done a tune up in awhile then it would probably be worth while to do one.