Probably a misfire, it could be in need of a tune up.
Possible cylinder misfire and/or failing engine mounts.
It could be (a) misfiring cylinder(s). Check the condition of your plugs and wires. Also, check if your engine mounts are not worn.
If it is running fine at high revs the most likely problem is an injector
Without much to go on, I would suggest you look for a vacuum leak, especially if the engine runs good under acceleration and only shakes and shudders at idle.
The most probable reason for the engine to shake at idle is the motor mounts may need replaced. This is generally from the front and rear motor mounts; however, the sides may need replaced as well.
Do u mean that the car shakes as you are driving, or just that the engine shakes when it is at idle ? Could use more info.
A 1998 Honda Civic shakes when it idles usually due to worn engine mounts. Open the hood and check the engine mounts. See if they are either cracked or brittle. Since the mounts can not absorb the vibrations it will be felt in the cabin.
Let it idle when moving and get back to us.
The idle control valve works by regulating the idle speed of the engine. The idle speed of the engine is usually controlled by the engine of the computer.
Replace engine cushions
Is it a 4 cylinder? Sometimes a 4 cylinder engine will shake a little extra when the AC is running and it's at an idle. You might be able to step up the idle a little extra but 4 cylinder engines are notorious for shaking when the AC is running.
get a room stop phucking in it