1996 Questions for all other cars revs

Engine Mechanical problem
1996 Questions for all other cars Engine Size unknown Two Wheel Drive Manual 90.000 miles

my peugeot 306 xsi, revs high, every other time I start the car and drive it, the revs high then low, up n down constantly the mechanic I use told me to have a laptop hooked up to see what the problem is, any ideas? Thanks. Dave