erractic idle with A/C off

Ok this is kind of a strange question. I just bought a 98 Honda Civic HX last week and have encountered a strange problem. With the A/C on the car idles normally at about 900 rpms in neutral, but when I turn the A/C off and let it idle the rpms jump between 2000 and 900. It almost sounds like it's going to stall. I thought it might be the clutch on the A/C compressor, but that would only make sense if it idled erractically with the A/C on, but it only does it while it's off.

Any suggestions? because I'm stumped.

Thanks so much.

check vacum lines and try this diy
http://www.superhonda.com/forum/showthread.php?t=144463

hmm strange.. my civic seems to have a similar problem.. when i start it, it will jump back and forth from around 1000 and 2000 RPMS then slowely its lowers to 1500 then 1000 after several minutes, is this problem the same with yours?