My car is pretty old but only has 100,500. I've had sparks plugs and oil changes donr recently but seems to idle rough with knocking sound coming from the engine when idling. Runs great but sounds a bit rough. Do I need to change out coil pack - a bit expansive? How do I know if need a change? Or is this related to the valve adjustment? Appreciate your feedback on this.

 

Are you sure that it is not one of the plug wires causing the issue? If it is actually misfiring and causing a check engine light, you can move the coil around to another cylinder and see if the misfire follows it. You can do the same thing with the plug wires and spark plugs to narrow things down. Also, there is no valve adjustment. Your engine has hydraulic lifters. I have seem them fail or cause ticking noises, but most of the time it is related to poor oil change maintenance.