i just bought this car recently . i'm the 4th owner . miles on the body is 307,560 but the last guy who sold it to me said they did a motor exchange so the motor is about 180 k miles .

the issue i'm asking about is that when i accelerate it's a slow start but once i really floor it then it becomes steady but it also staggers in the beginning . any idea of what's causing the staggering ? still runs smooth just annoyed with the staggering issue .

 

any check engine lights/codes? when was the last time a tune up was done (spark plug/wires/distributors)? also possible there is a fuel delivery issue or a dirty MAF, or even old fuel.

there is also a chance of a failing ECU but i would do the other mentioned above first before going the ECU route:
https://www.clublexus.com/forums/ls-...capacitor.html

 

How recently was the motor exchange done? Was it 100k miles ago? Or was it 2k miles ago and it's been troublesome ever since...?

With a motor swap, there are so many unknowns about the quality of the work done which could cause issues.

 

I'd check for engine codes first.

But a quick second thing would be new plugs, wires, caps and rotors. At that time I'd confirm robust connections of the coil harnesses.