Unplug the front sensor while scanning, it should go to about 450mv and hold. Then plug it back in. It should cycle between low and high. If it'* not cycling then there'* a problem, either a spark plug wire is touching the sensor wires, or the sensor is bad.

Danthurs, thanks again. So I unplugged the front sensor and it went to 450mv. This must be the bias. I attached the unplug plot, with a plot from the highway when I was ripping it. The voltage for both sensors went completely to zero. Do you think both sensors need to be replaced....its just odd that both are bad...probably right out of the both...could it be the computer is bad...I know I have condensation problems due to water leaks...sometimes there is condensation in the gauge cluster.
Wold fuel system cleaner or ethanol gas cause this? This is just too wierd, and I don't know nearly as much as you

O2 #1 pulled after startup


HighWay run. O2 voltage on left hand y-axis, engine rpm on right hand y-axis

Odd, when you get on it the O2 should be around 930mv, not way down, your running lean. If they have never been changed then you may want to do that and then rescan.

Something not right...thats for sure. The O2'* were changed just over a year ago (~6000 miles) with Denso or ACDelco. If you take a look at the first post, there is a laundry list of stuff I've replaced, checked etc.

Just to remind you, about 6 months ago when I pulled the spark plugs, all of the back plugs were dark black and all of the front plugs were bright white/grey. Same age, make plugs all around This has gotta mean something...I just don't know what???

If you got any other ideas...I can record other data too MAF, trim, etc.

Means your running rich on the rear three. It'* like the back injectors are bigger then the fronts. Or someone has changed your tune. Your O2s look normal on cruise and do what it should when you unplug it. But when you go WOT your AFR is going the wrong way. Hmm, now I'm thinking. Your scanner has a very slow sample time. Set your scan to only sample the front O2 and the RPM, nothing else. I'm starting to think the samples are not lined up because of sample lag. Actually, take RPM out and scan throttle position instead. If you move the RPM scan to the right to match the peaks and valleys, then it all makes sense. Scanning LTFT will also help.

The plots are in sequence from the same drive. First plot is in driveway and exiting neighborhood, 2nd plot on mainroad, third plot on highway. The o2 is on the right-hand y-axis. Be careful, comparing from plot to plot, the y-axis scaling changes. The sample time bounced around from 90-150 ms.

Not really sure what to make of the plots. The 02 went to zero volts again when i mashed it on the highway, then totally left-off the pedal.

Idle, and neighbor 0-100sec


Mainroad 100-200sec


Highway 200-300sec

The scans look good actually, lined up a bit better. The O2s move like they should, the LTFTs are in the correct range. When you get on the gas the LTFT is adding a bit of gas, but not to bad, the O2s look good. Then when you get off the gas the O2s drop because the engine don't need much gas to keep running when not under load. I'm not seeing anything that looks odd.

Thankss Danthurs. Well thats great that everything looks good, but I was actually hoping you would say something was wrong, so I could fix it. LOL.

Like I was saying the engine still runs like a top, great acceleration, etc, its just the rough idle and poor fuel economy I'de like to fix.

Let me know if you have anyother ideas.

Other then crummy winter blend gas, not sure what else could be wrong.

So I may have found the cuplrit. I pulled the fpr tube and smelled gas, not super strong, but the car was fitting for a while. I just going to replace it.

Can I buy the rebuild kit or should I pay about double for a whole regulator. I've seen multiple different ACdelco part #'* for my vehicle at websites, so im not exactly sure which one to buy. I am trusting rock auto, the rebuild is 2171598, full 2173294. I hope these are right.