I drive a 99 Civic Si and i just had all my belts replaced and i had my valves adjusted. The problem i am haveing is not constant but it is intermitant. On startup it wants to rev up to 2k rpm and then when it finally warms up it drops down to about 1krpm...but it will move between almost 200 rpm and 1500rpm at idle after a hard run. any idea how to fix this

 

Sounds like a vacuum line.