Ok, I have searched and read everything again but I still can't get my head wrapped around this situation. Most of the good articles are for SD systems or so old it is difficult to interpret.

BLMs are in order +/- 4 in cruise range.

Unplug and reset.

After some driving the BLMs are back in range for cruise. At idle I get very high BLMs of 145-160 WB AFR is 14ish. Which would be something I could deal with if it would just stay.

But here's where it gets strange. After everything is warmed up, coolant temp and MAT normal, sitting at idle all the sudden it starts pulling fuel. BLMs are at ~126, O2 mv is <100 and WB shows 17+. I have made small adjustments to the O2 error reduction gains vs airflow & Slow O2 filter Coef vs airflow trying to get it to stabilize but with no success.

I could deal with either the lean or rich condition, but it swings from one to the other for seemingly no reason. I suspect it has something to do with MAT or a bias that is coming in or going out. Any ideas??? Please!!!

 

Let me ask this a different way..

89 MAF system- 165 ecm- $6E mask- APYP code- Tuner pro editor

Does anyone know if there are idle bias or offsets which would make the ecm target a richer AFR idle at times and a leaner AFR idle at other times?

This is in closed loop, everything up to temp after running for a while. This "seems" to be related to temp but there are no notable differences in conditions when this occurs. the only variable I can see is possibly the volts drop a bit when the fans turn on. I can see how this may affect the idle richness but why the big swing in BLMs?

 

Try looking at the o2 constants. There are a few swing point settings for low grams/sec flow (idle) that you can use to offset the air fuel ratio that corresponds to blm of 128. Helps when cam has some overlap effects.

Does system still have air system in the headers?

 

This table can change it according to the CTS:

And this value can when AIR is diverted:

RBob.

 

Thanks guys.

Orr No the AIR system has been removed. I have disabled the divert or rather forced it to always divert via the "divert when mat <x" constant.

I am aware of the two tables you have pointed out Rbob. This condition occurs when the temp is above the settings in the coolant table and since I have forced divert, the value should always be subtracted from the R/L mean and H/L tables.

Now I have evened out the o2 tables (at idle) and it does have the effect of raising AFR. There is something I am missing.

I think I am going to confirm the fuel pressure is remaining consistent and reboot/clear and run it back through a few cycles and see what happens. Maybe it is a non-ecm issue.

I do appreciate the replies and please chime in if something else comes to mind.

 

I am following this thread closely, since MAF idle can always be improved upon. So i have more of a question than any help. What tables do you say that you have "evened out" at idle?
In TP RT5, i am assuming these:
O2 upper 0 Err Ref Slow O2 R/L
O2 lower 0 Err Ref Slow O2 R/L
Then there is one other table that shows values in-between the above tables.
O2 C/L R/L Threshold vs Airflow

Now these are all mVolt tables vs MAF, so i am assuming at 0 and 8gm/sec are the only points to affect idle. Now of course there are other O2 tables, but these are what i am looking at. With my ride, the values at 0&8 gm/sec
are 0.350, 0.398, and 0.451.

What i am getting at, is a recent scan at idle showed me some confusing #s. Now i havent done alot of tuning this year, since i acquired a '90 C4 with SD, so i been focusing on that. I will need some more scan data, but what i saw was low BLM, like 112, low O2 mvolts like 110, at idle at stoplight. Didnt get the WB AFR. Today drove car, and looked at WB at idle, showed like 15.5 with low O2 mV. I will try to get some more scan data soon, but part throttle BLMs looked decent.