P0171 Help!

[mazdalove99]

I have a 99 Mazda Protege that has been coming up with the code "P0171 System too lean" since Nov/Dec. In January I replaced a cracked exhaust manifold and put in a new battery. This month I replaced a cracked air intake tube and gasket and put in new spark plugs. Now while sitting at a red light the idle will be sitting just below 1000 rpm and then fluctuate and jump just above 1000 rpm and go back down, sometimes it'll jump up to around 1500 rpm instead. I'm beginning to think that it is a fuel related problem. I'm ready for this problem to be fixed! Any ideas of what it could be?

 

[p_ballermatt98]

Did you reset the ECU after repairing the cracked intake? Sometimes you need to set the maps back to stock so it can "re-learn" what it has gotten used to. If it's used to getting too much air then after repair it makes sense that it will see it as too little. Just disconnect the battery and turn the lights on, let sit for half an hour or so and hook it all back up. Hope this helps.
Almost forgot to mention that cleaning the EGR was what solved my fluctuating RPM's at idle, maybe that will help you as well.

 

[mazdalove99]

Yes, the ECU was reset. The repair was done on the 7th and the CEL came back, with the same code, on the 15th. I'll give cleaning the EGR a try and hope it works. Thanks.

 

[MikeyP1990]

don't forget to check for vacuum leaks, especially if you've done intake work. With the engine running listen for any hissing/whistling noises. check all the vacuum lines, and where the intake gasket is. rubber lines love to crack with age. You can also spray around with carb cleaner to see if you get a fluctuation in RPM's.

 

[mazdalove99]

There was a crack in the vacuum tube to the brake booster. =) Only time will tell.