Surging Idle (periodically) Overheating

Must be a common problem, I just bought a 91 Acura legend coupe and it's doing the same exact thing. This is my second legend and ive experienced the same thing with the first one I had, so I'm guessing this must be a common problem. The first one I had I changed the water pump, the thermostats, and bleed the system and it still did the same thing. Which lead me to believe it was the head gasket or something internal. So I decided to replace the engine and that solved the problem with that car. When the car started surging, I removed the radiator cap to relieve pressure and air was released and the engine idled at normal speed. So it has to be something internal with the engine like warped heads