Diagnose this problem Please., Studdering sorta. Options

[x_itchy_b_x]

Well this problem has always been there since i bought the car back in stock form.
Alright while holding the gas in like half way in 2nd or 3rd. at around 3k rpm. i just hold the rpms there and the car front of the car will raise and lower. and accelerate and decelerate in a pulsing way. like RRRRR rrrr RRRRRRR rrrr RRRRR rrrrr. lol im gunna say since im using stock ignition, IE coil and wires with larger injectors running more fuel maybe it needs more spark to ignite the gas better? then i was thinking. it also did this in stock form that that wont really explain why.
maybe poor contacts on one of the distro pins? or maybe iunno. can anyone give me there input.
Its not hindering performance cause once you give it more gas rather than holding it at a certain rpm it takes off and goes away?

[lagos]

yeah if the car itself moves, then its the motor mount. the motor is rocking back and forth as it tries to steady itself. when u give the car gas, it tilts back and settles in place. thats why you only feel it when trying to steady the rpms.

thatas my guess at least.