How much is it raising and dropping? Your IAC (Idle Air Controller) has a lot to do with that as well. If it's full of crap it will also cause your car to jump up and down in a cycle. It will run for about a second at 1500-2000 rpm, then bog down as if it were going to stall, then come back up for a second, then drop. Is that what you are experiencing? Or are you talking about more of a "load based" drop (i.e. when you're stereo is crazy loud, A/C compressor kicks on, power steering in locked position). Fill us in on specifically the issue you're having, and we can help a little more. The IAC is about $200-$300 but you can often take it out, clean it, dry it, and put it back in. On my old Prelude there was an adjustment to it which we had to change the first winter I had the car. If it's a load based drop, that's completely normal. Give us details on RPM levels and duration of each in the cycle and maybe we can help more.