O2 Sensor Lean...Tried Everything - Page 4 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-02-2008, 03:55 AM   #31
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To answer your question 1 redsled the engine hesitates while idling, but other than that it runs fine. Acceleration is smooth no cut outs or hard shifting or anything out of the ordinary. My instrument panel gauges..ie volts and oil pressure operating erratically and a/c turning off and on every two seconds when engaged, those are the only other issues. I did think it was odd though that when I plugged my intake tree on the plenum that there wasn't a flucuation of Mv on the O2 readout. It stayed right around 45 Mv plugged and routed normally. One other thing that is interesting...before I had the O2 code there were only a MAF code, an egr pintle position, egr flow, and QDM 1 & QDM 4. QDM'* were related to egr and maf so when i cleaned them all those codes went away. While cleaning those I took off the IAC to inspect and accidentally broke it compressing it. I replaced IAC with new one and seemed ok, but right around that time the O2 code showed up. The one issue I've had with replacing parts for my bonny is that at autozone and kragen the SSE comes up as a turbocharged on their system. I've double checked the maf to see if its the same for both models and it was. Maybe they gave me the wrong IAC. I'll look into that one.
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Old 04-02-2008, 10:23 AM   #32
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OK then. Sounds like it is truly lean at idle and NOT a false reading.

I think you are on the right track, looking at the IAC valve/motor, since it controls the air at idle. I don't have my manual with me and cannot find it quickly on alldata; but I rplcd my IAC a couple of years ago and there was a pre-install measure/adjust procedure. I will keep looking for a picture, etc. (I remember it had a picture for the measurement).
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Old 04-02-2008, 10:46 AM   #33
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Finally found it in alldata... assuming SC & NA are the same. Just wanted to be sure you knew about the measurement "A."
Name:  IAC.gif
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INSTALLATION:

1. If installing a new IAC valve, measure the distance between the tip of the pintle and the mounting flange.
  • o If greater than 28 mm, use finger pressure to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.
2. Lubricate the IAC valve O-ring with clean engine oil.
3. Install the IAC valve assembly.
4. Install the IAC valve attaching screws, and tighten to 3.0 Nm (27 in lb).
5. Connect the IAC valve electrical connector.
6. START the engine and allow it to reach operating temperature.
NOTE: No physical adjustment of the IAC valve assembly is required after installation. The IAC valve is reset by the PCM when the ignition is turned ON, and then OFF.
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Old 04-02-2008, 04:34 PM   #34
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So I checked the IAC and it measured at just under 1 1/8 in which is right on spec. I'm going to check the harness connector at the firewall and recheck all my grounds. At the ground point on the ICM mount there is only one wire and its closest to center of engine. Small gauged wire. Its the smallest guage wire I have under the hood. There are two battery grounds. One, the thick gauged wire, is mounted down by the starter. I have cleaned and reattached it. And the other is mounted on the fender wall with three other wires. Two medium gauged and one smaller gauged. The battery ground on the fender is the biggest of the four mounted at that location. Have cleaned and rebolted those as well. Am going to check grounds inside the car again to see if there'* any I missed. I have also noticed that once in a while a LEAN FUEL TRIM code comes up along with the LEAN O2 VOLTAGE code. I have the exhaust gasket and am going to install that today. Don't suspect it will help but never hurts to try. I also double checked the MAF by disconnecting at idle and found no change in O2 Mv. I know I'm repeating myself but, why would there be no change in Mv when I plugged the vacuum tree? Shouldn't that create a rich mixture? Making the o2 Mv go up....Just curious.
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Old 04-02-2008, 05:03 PM   #35
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Now, the vacuum is just a negative air pressure. There isn't any actual air flow when all things are good. It would probably make your fuel pressure go up, since the fuel regulator requires vacuum pressure to function. But I don't think that would make it run rich with the tree disabled/plugged.

With the bad idle symptom, it makes sense that it would be something other than an exhaust leak problem; something actually effecting the air/fuel mix at idle (throttle closed). Does the odor at the exhaust tip give you any hint of whether it smells rich or not (lean)?
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Old 04-02-2008, 06:49 PM   #36
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What'* the code you're getting, 44?
Did you check/clean the driver'* side ground bus?
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Old 04-02-2008, 07:21 PM   #37
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Im getting code p0131 oxygen sensor lean. Are you refering to the ground bus on the floor board next to the door rail?...Yes I've checked it and the one on the passenger side. Both are clean as a whistle with no signs of corrosion..I also did a wiggle test with all grounds connected to both buses. No change.
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Old 04-02-2008, 07:57 PM   #38
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I thought the 95'* used the OBD 1 two digit codes.
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Old 04-02-2008, 08:33 PM   #39
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according to my scanner(actron 9145) it shows 4 digit codes. has odb1 compliance but odb2 connector. all codes seem to be correct. when i cleaned my maf and egr both codes disappeared. i had a fuse on passenger side that controlled A/C and some engine controls that was blown so I put a new one in. My A/C started working and then I recieved the O2 code. Not sure if the lack of that fuse kept the o2 code from setting, but it showed up directly after i fixed everything else.
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Old 04-03-2008, 01:00 AM   #40
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actually technical ted the most 95 GM'* used a so called 1.5 OBD hence the 4 digit codes not 5 or 2 digit

and on topic im fighting the same inevitable problem only mine is a 96 i sprayed my car down top to bottom hitting every hose no surge or fall in idle i only recieve a P0171 lean bank one code and have done all the same short of replacement my MAF is up to spec and the reading on the O2 is good the IAC is measured to spec no wires touching the O2 i did a full tune up fuel filter fuel pressure check i did all positive and ground cables even where the mount to the fender i reseated my PCM plugs and the grounds in the car all looked fine and what little corrosion i had i removed and still had the code
so good luck
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