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.
It's likely that the idle needs to be adjusted higher, especially if it is an automatic.
Idle on a 1985 Honda Civic is adjusted through a idle air control valve. This valve is located near the intake. Adjust the valve by either loosen or tightening it.
The idle speed on a 1996 Honda Civic is adjusted using an IACV. The IACV, or idle air control valve, lowers and raises the idle by either being tighten or loosen.
To adjust the idle on a 2005 Honda Civic locate the idle control valve. The IACV and is found near the intake manifold. Open the top of the valve and tighten it to lower the idle or loosen it to raise it.
Idle Air Control Valve.
The Honda Civic loses idle at stop due to not have consistent air flow. The engine will run too lean and cause the car to shut off.
IF ITS JUST AT IDLE, CHECK YOUR IDLE AIR CONTROL VALVE IF IT HAS ONE.
The idle speed on a 2001 Honda Civic is adjusted through the idle air control valve. The valve is located behind the intake manifold. Open the cover using a screwdriver and tighten the valve to lower the idle.
Your 1994 Honda Civic will overheat when the thermostat is malfunctioning. The overheated engine can experience the idle to surge. The engine should be turned off immediately.
Because of the loss of backpressure if can affect the idle.
Idle Air Temperature sensor.
If the idle is erratic on a 1993 Honda Civic the IACV will need to be clean or replaced. The IACV controls the idle on the car and when it fails the car will not be able to maintain an idle.