It's not the motor mounts as the shaking goes all the way back to the exhaust. Exhaust shakes and puffs, sounds like a misfire.I rocked the engine back and forth minimal play which is acceptable according a friend.
I checked the plugs,timing,ground etc. I read that the knock sensor could be it, but I have no cel. Also when cruising and letting off the gas there is a slight jerk in the car. I just bought the car and this is the only problem with it. Looking to get it running right before driving it daily. I will be replacing the fuel filter and spark plugs with ngk plats soon and doing a reg tune-up.
Any ideas what else it could be? The car is fine until it warms up and then the idle slightly fluctuates between 500-800rpms.

 

checked the coils??? i had a bad coil but had a CEL soo still check it out, but it might be something else..... good luck

 

clean your throttle body. thats what i would do next.
stopped my idle from going all over the place including even stalling at times. plugs certainly wouldnt hurt either like you said.