1997 Honda Civic RPM racing with clutch depressed

For about two months I have been experiencing problems with my RPMs. It started after starting my engine (cold), in neutral, with the RPM revving from 1000 to 2500 and back. One extremely hot day, after driving over 15 miles, it revved over 4000 continually. I ended up having my car towed because even after turning the car off, it continued. The mechanics could only scratch their heads because the car wasn't symptomatic when it arrived at the shop. My latest incident happened in stop-and-go traffic. The RPMs revved continually over 2500. I found that keeping it out of neutral, in gear, while the clutch wasn't completely depressed helped. I don't know if the term is correct, but I think I was riding my clutch. I would let the clutch almost completely out (my engine would pull me along) while I kept my foot on the brake to control my speed. Not good. The reason I am asking today, is because I will be making a 700 mile trip soon. My car has only been good to me until now, and I am weighing my options about just giving up and buying new. Any ideas on how to fix this? I found posts that were similar, but don't care to spend hundreds of dollars fixing countless things if nothing works. Thanks for your time!