Hi, I have a idle scan of my 99Z that I have been having a little issue with. It has a intermitant stumble at idle. It will idle smooth and then it will stumble for a second or 2 and then return to normal idle. I have noticed that the gas mileage has gone down a little bit. Also it does not throw a 02 sensor code. The EGR/AIR has been deleted from the car for a couple years but not in the tune so it does have a code for that. But it never stumbled like this before. I am thinking its a o2 sensor but I cant be sure. Here is a live scan of the idle that my friend did for me with his HP tuners. Hopefully this helps.

 

Your O2 sensor waveforms say the sensors are not
happy li'l campers.

Now, my car has had that sort of sporadic idle miss
since it rolled off the lot. Maybe more of a hiccup
than a burp, but still. I believe this comes from the
proportional fueling (which swings fueling against
the O2 sensor indication to force more cross-counts).
But this is all set up predicated on a fast switching,
stock exhaust transport-delay setup as-shipped.

When your sensors get slow and your tubes get
long, the phasing of the counter-fueling can get
whack, overreact or react too slow to a bottoming
sensor after driving it into lean bottoming in the
first place.

I'd suggest diabling the proportional fueling as an
experiment, likewise an experiment where you lock
AFR and timing to nominal idle values (matrix these
two dimensions) and see whether one, the other or
both will kill that cough.

I've found that on my car prop fueling isn't needed
to get adequate switching (though "adequate" is a
matter of opinion, betwen you and the tailpipe
sniffer - tight dense switching means finer grained
chemical balance for the cats to work with, a slow
rich, slow lean feed means a lot more stuff slides
past the catalyst with nothing there to break down
against).

 

Wow thats a mouthfull. LOL!!! I will see if my buddy can come back over and try that out.