Why does my 300zx tt 91 engine sputter when I give it gas it did this earlier but went away now its back 500 miles into a syn oil change done 700 miles ago any ideas plugs changed about 1.5K miles?

Answer

It has nothing to do with symthetic oil, other than better stability and having no sludge buildup or other deposits, synthetic oil acts the same inside the engine.

Be suspicious of the fuel filter or fuel pump. If the engine is running well otherwise but only hesitates when you "get on it", it may be a fuel flow problem.

NO, Its defenetly your ECU, They are about 300 at auto zone.