I had a 98 LSV that did the same thing. I was driving to work one morning and then all of a sudden the RPM's started hopping from about 800 RPM's to about 1800 RPM's in traffic. Took it to the local mechanic. They couldn't find a vac leak or any real main issue that could cause it. So all he said he did was took apart the intake, cleaned out the intake pipe, cleaned out the throttle body really good and changed the intake filter. Fixed the issue. He mentioned adjusting the idle some, but never needed to do that. Not sure if this resolves your issue, but may be worth taking a shot.