I have a 1990 Honda Civic. I recently had issues with the fuel pump and the fuel injection system and had the pump replaced and a fuel injection service done. Since that time, when my car heats up after it's been running for a few minutes, the tachometer starts to jump at RPMs over 2500. It'll jump up to over 4000 RPMs and then back down. Does anyone know what might be causing this?

 

Is it just your techometer jumping or the engine's RPM really is changing?

 

Could be just a ground issue.