1997 Buick Regal LS with series 2 3800 engine

Been doing some troubleshooting on my 97 Buick Regal LS with series 2 , 3.8 liter v6.
When the engine is cold at startup the engine idles up as it should, then the idle comes down and the engine starts chugging, then idles up again, then idles down and does the chugging or roughness of the idle.
This happens when the car sits outside at night, but when the car is inside the garage over night , the chugging and idling up and down doesn't happen. After warmup, the engine runs fine. I do have 2 codes set; a P0140 and a P0141'
The codes are for the both the front O2 sensor and back O2 sensor. Performance on the street is pretty
good. It accelerates very well from stoplight s, etc. I took pics of the diagnostic engine data screens from my Autel OBD 2 scanner and I'm posting
them here on this thread so that others on this board could see and give input. Thanks.
George

another

Another

misfire screen

another

Do you live in the mountains? Map sensor looks like its reading for mountains. Maf sensor readings look ok about 4.5 g/sec. What are your o2 readings and fuel trims at idle and at 1500 and 2500 rpm?

Hello. Thanks for the reply. No mountains here. In South Florida. The data you see are at idle. Will get those trim numbers at 1500 and 2500 for you to look at.

Get map and baro readings from another vehicle if you can to compare. According to the chart i looked at the voltage has you at ~28000 feet elevation. I really think your map sensor is bad but check your wiring first with a fused jumper wire from 5 volt ref to signal should see data pid change to ~ 4.95volts if it changes to that the wiring is fine and your map sensor needs replaced

Correction
Koer at idle should be between .5 and 1.5 v

Koeo
4.5-5.0 sea level
3.0-3.7 at 9000-10000 feet

So check that to be sure in koeo

Hello,

Map reading with key on engine running is 1.24. This should be correct at sea levelz? Would that be correct, within the normal range?

Yes thats normal running what is it with key on engine off

Hello GMP440

Well, you will likely not find this helpful, but it is how driveability techs analyze (or should anyway) these faults.

You stated ...

"When the engine is cold at startup the engine idles up as it should, then the idle comes down and the engine starts chugging, then idles up again, then idles down and does the chugging or roughness of the idle. After warmup, the engine runs fine."

The Autel is poor scanner for this type of problem, but still... you're not using it correctly. You need to graph the data even though the tool greatly limits you. From there you can upload useful information.

I would not be trying to find a particular PID value that isn't "right". Instead you need to see PID values in context with the others. I know what MAP voltage I typically have seen, but what does that tell me? Not much. The context is missing. Being off by just a little will create large faults. Look for the faults and work backwards.

So why are the IAC counts so low? Given that (hint), you did not post the TPS voltage. The TPS voltage will auto-learn 0 %, even when it is too far out. I'm wondering if someone hasn't screwed around with the minimum air rate setting.

These early systems have much smaller operational windows than newer stuff. IOW, you have to make sure the basics are correct. The control systems cannot make up for things outside of a range that is not specified in SI. Things like the minimum air rate.

There are PIDs and there are PID controllers. The latter can be no better than the hardware it has at its disposal. That includes computational power along with motors, sensors, etc.

I believe the Autel will graph up to 8 (?) PIDS. A professional grade scan tool will graph the entire PID list.

Here is what I would suggest. Ask yourself what could cause the fault you describe and what PIDs would help identify it. If the engine is chugging or surging, what does that point to? What does the engine need to run smoothly?

You should find all you need in the "Engine Data 1" PID list. I've attached a list of PIDs that are in that list.

TPS voltage at idle is .43 volts.

More data.

Evap data.

bump