It'* long...sorry...hopefully good information.
Going into last weekend my check engine light showed up. Around the same time I also notice a blip in my rpm'* at WOT. Near 4K rpm there'* a superquick hesistation. Found out Advance no longer scans, went to Autozone for a scan. Code P0171 Lean Bank 1 (Front O2 sensor says the exhaust is too lean). Looked up the code in the FSM, it says to look for wires from the O2 sensor contacting the exhaust etc, possible O2 sensor needing to be replaced. Also says it takes two consecutive run cycles failing to turn on the CEL and three good cycles in a row to turn it off. I saw the light a few times, because it didn't fail everytime.
Wires checked good, O2 sensor on a real time scan tool was slow and sluggish on it'* responses. I have no idea if it'* the original sensor or not. Changed it with a new AC Delco, code still coming back quickly now. I'm at my mechanic buddys shop and he looks at it with his Tech2 scanner. He sees nothing out of place. Intermittent problem is becoming a constant. Whatever is causing the issue is going to be easier to diagnose when it'* a constant.
Next check is the vacuum lines. I had one or two that were cracked and one that was not making a good seal. Replaced them with some high temp silicone lines. Code still appears. I'm lazy and didn't check the grounds from engine to pcm as the manual said.
At this point it'* yesterday.and on my way to work I get the P0171 as usual and a P0336. P0336 is a crankshaft error, the system can't read the 18x pulses and defaults to using 3x (basically limp mode). Looking up the new code thinking it may be the root of the P0171, it says, check ignition coils, plug wires, wiring to ICM and crankshaft sensor wiring. I jump the gun and get a crankshaft sensor on my way home from work. When I get home and start following the FSM diagnosis...it has no mention that I need to change the sensor. Starting to pull my coils off to test the primary and secondaries, I notice all the bolts are extremely loose. (Month ago, I pulled them to help a buddy...he put them back on...apparently lightly snugged the bolts). I tighten them down and go for a test drive. No more blip in rpm, code P0336 never returned, P0171 is back again.
Ok, blip seems fixed. Being the only noticable issue..I'm happy. Only saw P0336 once and the FSM suggested checking coils. I found them loose..fixed as far as I know. P0171 still here..why? I spray TB cleaner around all the vacuum areas. No change. Extreme testing time...I hose off the engine while running with water. Serves two purposes, it'll show any vacuum/ignition issues and all the winter road dirt is being washed off. No change in the enging during the hosing. Hmmm doesn't seem vacuum related, or ignition related. Back to the FSM, check fuel pressure....while I know my fuel pump is making noise when I stop...it tests good. FSM suggests unplugging MAF sensor and driving it that way. (OMG you can unplug 3/4 of the sensors and these cars run seemingly fine). I drive for 30 minutes and P0171 is not found.
FSM says replace if the code doesn't return. I have a spare TB at home and change the MAF sensor (since it'* clean and does not look bad). No more code after 45 minutes of driving. Drove to work this morning, no codes.
Will continue looking for codes, this problem appears to have been a bad MAF. The MAF never showed a code or gave any indication that it was going bad. Even a trained mechanic that worked at Pontiac during the year of this car was unable to properly diagnose the issue with the information the car was giving. The Factory Service Manual had my answer through methodical diagnosis steps that a dealership mechanic would follow after the quick fix O2 swap didn't work.
I have ordered an Autotap scanner and it'* on the way. If I had it, I would have had files of recorded data and maybe could have seen the MAF sensor acting funny or giving different reading from it'* norm. I kept the sensor and plan on recording data with the good and bad sensors in...I want to know if I could have seen this issue.