I have a 1998 Civic HX with a CVT that runs great in park, but when you put it in drive it surges between 300-500 rpm's. Its very noticeable at a stop light and you must hold the brake on with lots of pressure.

Bad sensor somewhere. Will likely require a trip to the dealer to read the codes and fix.

. Check curb idle and set to specs. May only need to adjust throttle cable a small amount.

. Check for codes. AutoZone will do this for free.

. Test/replace the Ignition Control Module. AutoZone can do this for free.