Sorry for the impending long explanation.

I recently installed LT headers, and replaced the passenger side O2 sensor because it was giving me an intermittent "Right O2 Not Responding" code. It would work sometimes, and then randomly would quit, then come back to life. It typically quit when I was going down a hill and let off the gas, I am guessing the sensor was getting cold enough in that period of time to not respond/work. That is just a guess, and not the real issue, but should probably be known.

I installed a new O2, with a 24" extension for the headers, on the passenger side. I bought this one from amazon, AFS75 AC Delco.

Now for the open/closed loop behavior thing I am not sure about. Before the LT header install I could hold the car idle at 1500-2500 RPM (any given amount, but steady) and it would be rock solid at that RPM. Now after the LT install, and the new O2 sensor, I hold it anywhere in that range and BEFORE closed loop it will be rock solid like I was expecting. Now AFTER it goes in to closed loop the RPM will fluctuate 100-200 RPM and is noticeable in sound and looking at the tachometer on the dash.

Now here's where I get lost and want some insight. I put the old O2 sensor back in (the one that worked some times) and it gets a reading that seems random, anywhere from 0.450 to 0.800, and it will never go in to closed loop. All other sensors appear fine when comparing it to previous logged runs before the header install. Since it never goes in to closed loop the RPM stays solid at whatever I want. Put the new O2 back in and it will hit closed loop within a couple minutes, and goes back to the fluctuating RPM.

I am guessing before it would intermittently go in and out of closed loop due to the bad O2 and that is why it would appear to be rock solid RPMs. Is the fluctuating RPM thing normal, or are there other sensors I should be concerned about? IAC, TPS, MAP, and driver's O2 sensors compare to previous logs. Something to note, the new passenger side O2 sensor does not bounce around as quickly as the driver's, concern? The car did run very rich prior to, and after the header install (with the bad O2). Since winter hit I am not able to drive around with the new O2 in.

As a side note, there have been a couple times while driving, and once while idling, where the car seems to knock hard for an instant, stumble, almost die, then come back like nothing happened. The knock count goes crazy after this, such as the one when it was idling it shot from 4000 to over 10,000.

All sensors were read with freescan.

EDIT: probably should be noted the EGR, and AIR pump have been removed.

 

Does Freescan report open/closed loop status? If so, that would eliminate the guessing.

The engine should run as smoothly in closed loop as it does in open loop. You appear to be concerned that there is an RPM variation when you try to hold it steady in the 1,500 - 2,500 range under no load. Is this the only symptom of a problem you are seeing?

What do the long term fuel corrections look like? Or is this not possible to report because you can't drive the car in the winter?

 

Yes it does, but when I was noticing the O2 problem I was not checking the state of closed/open loop. Hence me guessing, and now since the old O2 does not go in to closed loop at all it kinda beats the point of running down the road with it to try and get the same "Not Responding" code again.

That is exactly what I am concerned about, and yes it is the only symptom. Basically it's a behavior I have not noticed before, and want to confirm it's either normal or not.

With the new O2 I do not know, haven't had a chance to drive down the road logging and probably won't till next weekend. With the old O2, steady throttle, 55 mph BLM left and right are 118 to 124 (but steady), Integrators bouncing between 120 and 134, BLM cell 6 or 10.

If it would help I can upload my log files with the headers in, and the old O2.

The primary reason the varying RPM concerns me is I can hold the throttle at a given RPM in open loop, it'll be perfectly steady and freescan shows < 50 RPM change. Then once it changes over to closed loop, with my foot still on the pedal during the switch, it's an instant noticeable change in sound and RPM and freescan reports ~150 frequent RPM variance.

 

What is the IAC valve doing when this is happening?

 

I know these are hard to compare because they are not under the same conditions, but maybe there will be something that sticks out from the ordinary under the given conditions.

Old O2, 55 mph
IAC = 74 to 78
TPS = 22
MAP = 0.72 +/- 0.03

Old O2, 42 mph
IAC = 65 to 69
TPS = 7
MAP = 0.37 +/- 0.01

New O2, No load, in park, ~1600 rpm
IAC = 52 (steady)
TPS = 8 to 9
MAP = 0.28 +/- 0.01
BLM Cell = 16 to 18, mostly in 17
BLM = 122 to 128 (starts off at 128 both sides, then drops to left 125, right 122)
Integrators = 114 to 132

New O2, Idle 650 rpm in park
IAC = 38 to 42 (38 once it was totally warmed up)
TPS = 0
MAP = 0.36 +/- 0.01
BLM Cell = 16
BLM = left 122, right 116
Integrators = 124 to 134

 

Since sounds and behaviors are impossible to diagnose via text/internet, here is a video.

Again, this happened after I replaced the passenger side O2. I can't put the old O2 back in and compare because it does not work anymore and will never go in to closed loop.

Sorry for the crappy video quality, but it gets the point across and is the only camera I had.

http://www.youtube.com/watch?v=jkGOwwJGJ6g