My 93 Civic was doing that & it turned out to be a bad coil. Easy fix for me once I realized what was up. RPM would jump up & down violently with no change in true engine RPM at first. After a wile it would randomly jump around & the engine would lose RPM & sometimes sputter to a stop. If I let it sit & cool off for a while it would start up like nothing was wrong. I figured that my coil was cracked & failed when warm.