Halik,
Just go to the site that you recommended (
www.twinturbo.net) and ask in the tech section. 1990 has too much service bulletins from Nissan to list here.
As an example :
Service Bulletin #: FC0004794
Date of Bulletin: Jan. '91
Model: 300ZX
Year: 1990
Summary: Excessive initial timing advance, index notch on camshaft damaged, R/R crank angle sensor, camshaft and cylinder head--1990 300ZX CM
The problem was that the left cylinder head of a certain production # range of early Z cars ('90) was mis-machined. This caused the CAS to be thrown off in its readings of cam timing, so the symptoms are usually very sluggish performance or detonation. Eventually the readings of the CAS stray so far (for reasons unknown to me) that the symptoms show up when the cars have some mileage on them. I've heard of some having this problem and they replaced the CAS, but the CAS was expected to fail again, because the root of the problem is the badly machined left cylinder head.