The engine shakes when stopped. Rough Idle. - 2002 Nissan Quest

OBD Tools 365 Days Shop
A rough engine idle can come from a variety of causes. During the winter months, cars may have a harder time starting and will shake when first turned on. This form of rough idle can easily be mistaken for other problems. Engine idle problems can also be attributed to malfunctioning components, such as spark plugs. Holes in the air intake valve can also cause a rough engine idle because of excessive amounts of air being drawn in.
The rough idle of an engine can signify a power loss in the car. This loss of power could lead to other problems, such as excessive gas consumption. This lack of power can also lead to additional wear on other parts of the car. Ignoring problems with the engine of can lead to a massive breakdown that will require you either to make costly repairs or replace the car entirely.

You can use obd2 tool to check the engine system.

Rough Running Engine - James on Engines #2 - Bell Performance

https://www.bellperformance.com/blog/rough-running-engine

Apr 21, 2015 - When diagnosing an engine with a rough idle, there are certain things that must be ... If the problem does not reoccur, the codes will be erased by the computer. ... when accelerating the vehicle, which causes a higher fuel demand. .... it was water in gas...added added Gas LineAntifreeze/Water Remover.

run the fault codes
check for vacuum leaks on all vacuum hoses
check fuel pressure
use quality injector cleaner

When was the last time a full tune up have been done? A bad intake gasket would do that.

You do have a light flashing, so one would think you
already checked for codes & knew the system with
issues

Need to discuss all that at a repair shop

either on removing the spark plugs and the HT Leads might you mixed them up somewhere bet six,seven and eight.

Well this could be caused by a number of things. But the most common cause is an "engine miss." You could have 1 cylinder that has stopped firing. This will cause a very rough idle and very possibly shake or shudder whenever you accelerate. Another cause may be a main "vacuum hose could be disconnected" from it's port. Vacuum leaks cause engine shake at idle. Check for loose, cracked, or disconnected vacuum hoses under the hood. The third and least likely cause is a "broken or worn motor mount". If the engine is not securely held down in place by all the motor mounts, it will vibrate excessively and cause a shake at idle. The engine miss and motor mount problems are 2 issues best left to a professional to tackle. But as I said, you could tackle the vacuum leak issue yourself by checking under the hood. Hope this helps, good luck!

This can be your Idle control valve, when you turn the air on it puts the engine under load and your computer will increase the idle automatically to prevent the engine from cutting out.
When you are standing still and the car is shaking, by touching the accelerator very softly does the shaking stop? If so check the idle control valve.
I hope this will help.
Regards
Sam

What car , and year and engine? What color smoke?