1995 GT - O2 Sensor indicates lean

Doctorj77 · Oct 4, 2018

So I been chasing down a vac leak for past few weeks. Would have a idle surge issue after car warmed up, hanging around 1500rpms and then would slowly fall. I chased down the IAC - replaced that, EGR - hooked that up correctly, TPS - verified voltage was at .99v, cleaned MAF, cleaned TB, replaced distributor cap and rotor, and replaced broken gaskets on the TB, spacer, EGR, and the car would still have the surge issue. So this obviously had to be vac related.

One thing I tried tonight, I put the stock airbox back on, and actually it seemed to tame the surging idle a little better, but was still there. Then I got to thinking, maybe its the intake. So I took the upper off and discovered that on the lower, the bolts holding it in were finger tight, if even that much

. Long story short, the person that had the car before me, apparently reassembled the intake without torquing any of it. So I followed the torquing sequence, followed by the upper intake, and re-assembled the spacer, TB......etc. Put it all back together.

Test drive - car seemed to run great. My surging idle was gone, and overall just seemed to feel a little snappier. Could just be a placebo effect I know but the car did feel better. Anyway, got it on the highway and started feeling some bucking/detonation and then the CEL comes on. Pulled the codes and I am getting two codes I never got before

172 - o2 Sensor circuit indicates system lean (right side)
176 - o2 Sensor circuit indicates system lean (left side)

Now, list of mods: Edelbrock Performer intake & 190 heads, E303 cam, FRPP shorties, O/R H pipe, stock MAF, BBK 65mm TB, BBK CAI, and a SCT chip with bama tune for all this. I'm wondering that if by going back to the stock airbox I caused a lean condition. Now knowing that my vac leak was likely due to the intake bolts being so loose, I should probably go back to the bbk cai. In case I'm wrong, or its not because of that, what else causes the 172/176 code?

ttocs · Oct 4, 2018

I would go back to the CAI and then I would start with the bama tune and I do not mean send it back and have them dick up another one for you. I have heard more bad then good about them but unfortunately only after I tried them out of desperation. They had all my options in their drop down menus and it was not an insane combo/off the shelf products but it still ran horribly. I limped to a dyno and was much happier on the drive home.

evilcw311 · Oct 4, 2018

Bama tunes is garbage. Finish verifying if you have a vacuum leak first with a smoke test

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96blak54 · Oct 5, 2018

Perfect reason to blaze up a cigar!

Doctorj77 · Oct 5, 2018

I'll throw the cai back on tonight and test. I know the bama tunes are typically not well received, and maybe I'm lucky, but I never actually had a problem with them. Aside from this lean condition that cropped up, the car ran great. My surging idle was non existent, and when I come to a stop, no more rpms hanging around 1500 and slowwwwly dropping down. Comes down to 900-950 without any effort. I could be wrong, but don't appear to have any symptoms of a vac leak anymore.

Since the intake bolts were dogchit loose, I'm wondering that by correcting it, I might have affected something else. After a road test, if it still acts up, I'll move onto a vac test. I actually have a smoke machine somewhere...... have to dig that up.

ttocs · Oct 5, 2018

I had to think if the last guy was too dopey to tighten the lowers bolts I would take the valve covers off and make sure the head bolts and every other bolt is tight.