1990 300zx missfire, no code

[SpeedFreak_Josh]

I've posted before of this problem but have recently noticed something.I have a 90 300zx tt with a miss that gives off no code. I've checked the ptu, coil packs/injectors(visually) and replaced the spark plugs and ran the self diagnostic check. NOTHING.I noticed while coasting at 20mph or higher up to 45mph or so that the tach jumps around idle. 750-1150rpm. It smooths right up when I come to a stop. This makes me think that I have a problem reading the air charge. What do you guys think?Thanks

[Q45tech]

Dirty or improperly set IAC valve?

[ttinfinitiM30]

my 93 mazda currently jumps from 1000-1500 at idle. my prob is that my o2 sensor is giving no signal. the check engine light wasnt lit, but when hooked to a scan tool it said the o2 problem. id try using a scan tool (any good garage should have one that works w pre OBD-II) cause theres several things that could cause that kinda problem. good luck

[SpeedFreak_Josh]

Dirty or improperly set IAC valve?

I don't have a problem with the idle. Actually i have a miss while cruising. I've just noticed that the tach jumps around when I put it in neutral while I'm still at speed. If my IAC was missadjusted wouldn't I have an eratic idle? Mine is smooth.

And I did the self diagnostic check on the 02 sensors and they operated within specifications.