97 240sx Engine Shaking/Puttering Sound

[supradeluxe]

Hi all, I really need help on this one, my 97 240sx 80k stock KA original miles was recently running pristine until I notice when at idle in park or idling in drive at a stoplight, I can feel my engine shake enough that my steering wheel would shake inside the cabin. If I look under the hood, I notice it would shake, stop, shake, stop very oddly. ENgine sounds normal, but it would shake. Idle seems ok, but ever so slightly itll go up and down by 100rpm difference nothing very noticeable but I predict its just starting to show symptoms. Car doesn't seem like it lost any power either but could be a starting symptom. Anything I should look into? I figure it wont be motor mount because car doesn't shake when driving and stopping, only shake at idle and idling in drive. I have included video of engine and exhaust sound not normal at all. Please help me direct in right direction. Thank you
https://www.youtube.com/watch?v=IyjcygJNL9Y

[Ilya]

While running, disconnect the injectors electrical connection one by one to see if one causes less of a change than others.

So unplug one, check the effect, replug it, move on to the next

[supradeluxe]

Found out it was the intake manifold gasket, everytime spray brake cleaner in there, engine will sound better and hissing sound stops