Buick 3800 P0171 code [FIXED]

I have a 2002 Buick Lesabre with the 3800 Series 2 engine. It has 205,000 miles and has had multiple issues in the past. Rotted out filler neck, canister vent selenoid, purge selenoid, all related to evap leaks and malfunctions. The battery was also tested bad and replaced. It was 11 years old. The car had long cranking issues and was idling rough. I smoked the intake and found leaking intake gaskets. I replaced the intake with a Dorman and cleaned the throttle body which was filthy. I also cleaned the MAF sensor. The car was barely idling so I did some testing on the MAF and found it to be unresponsive to throttle inputs. I replaced it with a new Dorman MAF and disconnected the battery to reset the learn procedure. After reconnecting the battery, the car started great and idled almost immediately normal. It is now running great, but just threw a P0171 code last night after three days after the new MAF install. The instructions with the new MAF sensor stated that the check engine light may come on during the learn procedure with the new MAF, and to simply clear the code and continue to drive the vehicle. The o2 bank 1 sensor is flatlined lean at idle but does respond to throttle.

I think the best way to go is look at the O2 sensors and the short and long term fuel trims for both banks at idle speed and raised RPM

Check the upstream O2 sensor activity particularly on Bank 1 (B1S1) when the engine is warm it should jump up and down between 0.1 and 0.9 and back to 0.1v at least once per second.
Compare the total fuel trims for each bank at idle with fuel trims at raised RPM. With a vacuum leak the fuel trims improve at higher RPM, with a MAF problem the reverse occurs.

Hi Andy. Hooked up my scan tool this morning and checked the fuel trims. The short term was +14 and the long term was +16 at idle. At 1,500 rpm, the short term went down to -2 and the long term went down to +14. I didn't do a fuel trim reset, but I believe it has been running lean for a while that's why the long term stayed about the same. The P0171 started after I cleaned the throttle body. It had a lot of carbon and dirt on the throttle plate. I believe this was masking the lean code by not allowing much air in at idle. I am going to smoke the intake tomorrow and check for leaks.

Yes vacuum leak is now in the frame.

I smoked the intake and the brake booster o ring was leaking. Fixed that and installed a new Denso upstream O2 sensor. The fuel trims almost immediately dropped to zero and the new sensor is cycling properly. I took it for a drive and all but two monitors are ready. I am going to drive it more tomorrow and see if the other two monitors set. (Heated o2 and the evap). I'll post back. Thanks for the help, Andy.

Something really satisfying when you get the fuel trims close to zero on an older car, I had vacuum leak in yesterday a cracked purge connector on an MG TF -- after I improvised a fix the fuel trims went right back to average zero.

I did the GM driving cycle early this morning(at least tried to without being forced off the road). And all the monitors are ready except the evap. That may take a while to run from what I understand. No check engine light or lean codes. Gonna have the daughter take it to emissions tomorrow and see if it will pass. I believe that for 2001 and newer vehicles, one monitor not ready is acceptable. I read that evap won't run if the temp is below 30F or above 90F. Probably why they allow one monitor. Will post back when I get the emission test result. Looks promising.

The wife ran the Buick through emissions and it passed....YEAH!!! It had four issues; vacuum leak, dirty throttle body, bad maf sensor, and bad o2 sensor. I guess one fault led me to another. Have to expect issues with over 200k miles. The car is running like new and starts and idles well. Have also noted a noticeable increase in power and acceleration. I had no trouble winning a race with a souped up Harley. Thanks for the help, Andy. I may be back in the future for additional issues as they arise. Take care, Jim.