This could be the result of one or more vacuum leaks, low transmission fluid level, an internal engine malady such as a seizing piston ring.
why does my car shudder when idle?
it's because your car is not getting enough air to cool down.
if you are idling the vehicle for 10 minutes or longer, shine a flashlight at the bottom of the engine compartment and check that you don't see any hot spots; these are quick signs of overheating. the clutch should be making full contact with the flywheel, both on its release and on application, which means it will “walk” up to meet you as you press it in idle mode. you can test this by adding power to your parking brake during idle – if there is no “clicking” sound when pulling off idle mode after releasing pressure from your parking brake pedal then this could also indicate an issue with the transmission lock-up coil or
why is my car engine shuddering?
if the engine is shaking more than normal, it might be because of transmission problems. one sign that your car's transmission is having problems is that it also shakes or shimmies while you're driving on the highway. there are many possible reasons for this, but one of them may be incorrect transmission fluid levels. start by checking the fluid level and adding more if needed (with an owner's manual for expertise).