I have a 2002 Mitsubishi Galant that is having some odd issues:
While driving the car gets warmed up and running well. Once driving a few miles it will start to lunge slightly when the foot isn’t on the gas. In other words, if I’m driving 45MPH and take my foot off the gas there will be a little lunge to deal with. If the car is in park or in neutral the engine will idle 1000-1500RPM higher than if it was in drive with my foot on the brake.
Other than that it drives fine. There are no other issues.
My 99 Galant 4cyl had valve cover gasket leaking into spark plug recesses. Tune up with wires and gasket fixed it.