First, I recently found the forum and have definitely benefited from the knowledge here. Ok I got the dreaded P0171 lean rail one error with no other codes on a 1999 SE K vin. The symptoms are car starting hard, once started it runs well at low RPMs, like enough to drive around town. But If you hit the gas hard the engine bogs down. I've changed the intake 02 sensor, cleaned the MAF sensor and changed the fuel filter. After the fuel filter change (long overdue) the car ran slightly better, but still bogs on the top end. In reading through some of the posts here on a hunch I disconnected the MAF and tried starting 3 times. On the 4th try the engine ran and though the car is still sluggish (obviously with a disconnected MAF) lo and behold I have top end again.

I'm thinking this narrows it down to the MAF sensor, but wanted to run it by you all to get your input, before I bit the bullet and purchased a new MAF sensor.

Thanks in advance as well for all your past help! Fantastic forum.

I wish it was that easy.

Lean Bank 1 aka P0171 is a good friend of mine.

Typical causes:
Corroded and or loose battery cables (poor power supply causes the maf to read badly)
Vacuum leak
Bad maf sensor - by unplugging the computer defaults to predefined and usually rich tables to run from.
Backwards connected evap soleniod. Check that the fitting labeled "CAN" is routed to the canister in the fenderwell and not to the throttle body.

Start with the vacuum leak. I've seen this code pop up several times due to vac leaks.

Ok, I'll give a good thorough check to vacuum, battery terminals, and canister. At this point I'm pretty much willing to start at ground zero and recheck everything in case I overlooked something in the first 3 go arounds

Thank you both for getting back so quickly, I appreciate your help. This forum has given me a ton of good information. Can't wait until I get through this issue and can be giving info instead of needing all the help.

Ok checked all of the below and everything looks good. Electrical is fine, new battery and verified the posts looked good. Checked vacuum hoses for proper connections and made sure they were clear and all is ok. Found a known working MAF sensor and swapped it in. Still same issues. Any ideas on where to go next?

When you looked at the battery cables, osrry..we should have mentioned to remove the bolt and the rubber boot. Even with clean terminals it is possible corrosion is in the cables.

Next thing to do is to head under the car. Right behind the AC compressor is the main engine ground from the battery. Remove and ensure it and the block are both clean.

Remove the passenger wheel and splash shield in the wheelwell. Behind the motor is a ground attached to the block. This is a key ground for the sensor. Check that both this and the block are clean.

Thanks again Bill. I did replace the negative side bolt so that'* new. I checked some of the other grounds, but not the ones you mentioned, so I will give that a shot tonight. The car has 170,000 so corrosion definitely would be a possibility.

Here'* what happened to me if it helps any.

I decided to change the battery. Poof P0171, looked in the FSM and tried all the usuals. Posted and almost no one had experience with it. No common fixes. Foghorn posted and mentioned he found the main ground to cause this on his 97. Checked and cleaned battery cables and it helped slightly, didn't 100% fix it though. In looking closer the corrosion we deeply embedded into the cable. The only solution ended up being cable replacement of all three cables. One cable didn't fix the issue 100%. At the same time another member had a loose battery post (aka cracked battery) and that caused the issue for him.

A few months later I worked on the car and the P0171 appeared again. I retraced my recent steps and found the evap soleniod vacuum lines to be backward, causing a vacuum issue.

Another friend has had the code for a while and I haven't taken a good look at the car. It has new battery cables and some vacuum fittings. Soon, I'll be figuring it out as a new maf sensor didn't fix the issue.

Very interesting, I recently changed the battery. While I'm hitting the grounds I'll give the battery cables a good going over and changing them is a relatively cheap option even if I don't see anything obvious.

Here'* were I'm at now. While rechecking vacuum using carb cleaner, I'm noticing that if I spray where the EGR valve bolts on that the idle smooths out. Not trusting the results I've retested a number of times. Start car and get rough idle, spray where egr mounts engine idles smooth.