is suspension suposed to be so stiff

Does not look like it is standard equipment to have air suspension on an '86 Nissan 300ZX. There are lots of kits to convert, but: From: http://www.ehow.com/list_7492151_specifications-1986-nissan-300zx.html.....The suspension consists of a front independent setup with MacPherson struts and a semi-independent rear axle guided by trailing arms. Front and rear anti-sway bars measuring 22 mm aid in cornering and with controlling body roll. It's a sports car that corners well and will have, relatively speaking, rather stiff suspension