Transmission or Engine Problem?
 

Hi guys. Im new here. Im sure these questions have been answered before, but I am having a hard time finding a solution to my problem. I recently purchased 2x 300zx: 1 300zx 2+2 non turbo with JDM motor swap and then decided to just buy a 1990 300ZX Twin Turbo.

It was a bit of an impulse buy as I always liked these cars but I am having a bit of problems getting it to run properly. For one, the twin turbo that I just purchase is must slower than the heavier non-turbo. Plus, there is this "THUD" sound when I pop the clutch. Once the clutch is engaged and the car is in gear, it jerks like crazy and then it smooths out. It does this everytime I shift basically (more noticible in lower gears) The car idles rough unless I let it warm up a bit as well. The guy I bought it from said that these issues were all from two bad coils, but I replaced them and it hasnt done anything.

I imagined that a twin turbo with 300hp would be quite fast, but its not fast at all. Its about as fast as an accord. What could be the problem here? Engine problem or is it transmission? Could it be a bad clutch? Flywheel? or something to do with engine? Electrical? I have no clue.

Is it a stock TT model ? (or you would have to check modifications eventually done)
clutch wouldnt make idling rough
but the clutch could be broken too for the "thud" sound
do you use gasol ?
does your seller look for a job ? like commercial ? :p

It is stock turbo. No, the clutch wouldnt make the idle rough. Im just saying that is ONE of the problems. I think there are multiple problems with the car.

Run codes, the thud is most likely diff bushings, if the 120k timing belt service hasn't been done do it, check the plugs and compression, ohm the injectors and go from there.