1998 LSS: P0171: System Too Lean (Bank 1)

I recently bought a 1998 Olds LSS (112k, not the supercharger version). I'm struggling with this dang P0171 error code. I've found a lot of conflicting information online about it, so I'm hoping someone can point me to the next step. Here's my entire experience so far:

1. After buying the car, the tank was full of a generic gas station's 85 octane. Next morning the Check Engine light was on. Manual said the check engine light may come on with poor quality gas, and to use 87 octane or better. Drained tank, refilled with 91 octane from Chevron. Drove 50 miles. The Check Engine light stayed on.

2. Got the codes read at AutoZone (two P0171: System Too Lean (Bank 1) messages stored). Research online appeared to link this to the O2 sensor. AutoZone said Bank 1 indicated it would be the one under the hood. I replaced this, blanked out the codes, and the Check Engine light stayed off for 8 or 12 hours. Hooray, said I!

I got safety and emissions done, and passed. Just as I was ready to relax, the light came back. Same error code. Well, at least it was off for the emissions test so I could register it...

3. I did some more research and decided to try a couple things at once. I cleaned the MAF sensor (properly, with MAF cleaner). I replaced the fuel filter. I added fuel injector cleaner to the gas. I reset the codes and hoped. A few hours later, though, the light is back on. Same code :banghead:

I can't find anything else wrong with the car. It runs and drives smooth. At this point what I find online is that I likely have an air leak somewhere. I'm only a backyard mechanic, so the prospect of spending hours trying to find a tiny vacuum leak makes me start thinking about paying a real garage.

Any advice for me on what to try or where to look next? I'm willing to learn if it saves me a couple hundred at the mechanic :grinyes: Thanks in advance!

Welcome to AF. Low fuel pressure, air entering the engine behind the maf not metered , any vacuum leak, bad maf, are some of the more common causes. Bad 0 2 sensor, it should have a full scan to properly diagnose this. How about the pcv, has it been recently replaced?

Unfortunately I have no idea when (if ever) the PCV was replaced. All I know about the car is that it sat for a while, ran out of gas at some point, and though drove nice, needed some work. I plan on getting the fluids flushed and replaced professionally soon; pretty sure the heater core is clogged (still circulating and keeping temps good elsewhere, though), and betting the transmission fluid isn't much prettier.

Aside from this P0171 problem, so far I've only had to replace the battery ($90), replace the washer fluid pump ($21), replace the coolant level sensor ($38), and hook the cruise control back up. I was hoping this one last issue was something else I could handle on my own, but if I can't, I can't.

A friend said it could just be dirty / varnished fuel injectors, and recommended Sea Foam, which I'm now running through my tank. Funny enough, after completely filling the tank today, the CEL went off for about half an hour. In my old-school way of thinking, that seemed like perhaps a weak fuel pump, but maybe it was coincidence. Think it might be as easy as letting this additive stuff do some cleaning, or is there a specific spot I should check for air leaks? I didn't see anything obviously cracked or loose, but can't imagine it's too huge if the light goes off sometimes by itself.

As suggested by maxwedge you need to check the short and long term fuel trims with a full function odb-ii scan tool which may indicate what direction to go. There are quite a few possibilities unless obvious.

DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero (+) indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero (-) the PCM is reducing the amount of fuel to compensate for a rich condition.