I recently had one coil pack go bad. The engine idled rough and skipped while driving,no check engine light. Replaced the one coil pack and all the plugs.The car has 220,000 on it. Ran great for about 2 weeks then started missing while driving but idles smooth and revs fine, no check engine light. Pulled connectors off cop one at a time could not find bad cop. Checked for vac leaks and checked intake for leaks. The motor now sounds like a diesel while driving (valve flotting). In park the motor revs fine no rattling only under a load. I run hi octane gas in it and this is same tank of gas before the problem begin.