spark plug gap
Can also be a vacuum leak.
Yes, when idling and driving.
Sounds like a misfire caused by electric supply to plugs.
Loose motor mounts.
A clogged muffler can.
Is the car running ok? If yes and its only the vibration that's an issue most likely cause is motor mount(s)
There are a few reasons why a car shakes when idling at a red light. Some reasons could be the ignition coil, motor mounts, or spark plug problems.
It depends on how long you are idling, or how fast you are going. If you know you are going to be idling for a long time, it's best just to put your car in park.
i would really like to know myself
Yes, either can cause a shake while driving.
If it happens when you are driving fast (60-70 MPH) it could be that your wheels are out of alignment.
Your power steering pump and or steering box may be about to give out on you.
This is a very general answer, as I don't know what "running bad" means. I would start by changing the oil filter and filling it with new oil. I find that quaker state is the best. Next, I would change the spark plugs. Bad spark plugs and low oil can often cause a car to jerk and shake whether your driving or just idling.