87 civic 1.5L. This car runs great until it runs awhile. Once warmed up the RPM's begin to erratically surge up and down and while at a light, or on the freeway it stays up at like 4,000rpm. And then when you shut the car off it stays running and makes weird noised and runs very ruff. What is going on with it? I know this is really hurting the engine, please help.

Vacuum leak. If you have the Si model this is caused when the map sensors wire has a short in it. This is going to be mounted on the firewall. It will be a yellow wire. Trace it to see if any of the plastic has come off it. Also. Check out redpepperracing.com they specialize in 1984-1987 civics and crx's. Look me up when you get there.