Iv'e got a 95' Civic Si. If the car has sat for an extended period of time, and i start it up....the tach jumps up and down between 700-3000rpm when im at idle. After a few minutes of driving though, it's back to normal. Any ideas?

 

fast idle valve thingy. not sure the name
but clean out your IACV, use some carb cleaner in a spray can