you might want to check the fuse on the passenger side-right side of glove box. If that is good, i would just replace the vehicle speed sensor (about $60)
pretty easy to install.
have same problem with my 98 honda coupe. the vibration idling only happens every now and then. other problem is when i hit the clutch my RPM drop low and jump back up to regular idle. once rpm's go back then i get the vibration.