2001 Honda Civic Cool Engine startup

Hello! I've been having an issue with my Civic for a couple of months, and am getting annoyed by it. Whenever I start the car after having had it sit for at least an hour or 2, after a minute the RPMs drop below 1000 and the engine starts to sputter. A few seconds later, it will jump up to 1500, but degrade down again. This repeats for a few minutes until the engine has warmed up a bit. After it's warm, then it is fine until I turn it off and have it sit for a while. My mechanic mentioned that I'd have to leave my car with them for a bit so that they could isolate the problem, but I can't do that (I need the car). Is there anything I might be able to check to see what might be causing the problem? My experience with the mechanics of cars is very limited, but I can see what I can try or have my mechanic focus on.

Thanks!