I have a 95 Corolla with 242,000 miles on it. It has had a rough idle since 110,000. Not an ignition miss, but a rough idle. I did a compression test, checked the camshaft for wear and looked for vac leaks. Found nothing. And at times it will smooth out so I ruled out a mechanical problem, ie something out of balance. I'm thinking its fuel injectors. I have added cleaner to the fuel without any noticable improvment. And at the cost of replacing the injectors, its not going to happen. It passes my states emission tests and runs just fine. Its a well engineered car and except for the noise caused by the vibration, it gives a great massage. Cudos to the Japanese for their engineering.