Cel p0171

Hello Everyone,

I am new to the forum and I was hoping to get some help with this check engine light code P0171(uhm). I have a 2007 Mazda 3 touring. It has about 150k miles on a 2.0l engine. It's a manual transmission with California emissions. The car is completely stock with no aftermarket upgrades, just replacement parts. I have had the cel code p0171 for about 3 months now, and no other codes have presented themselves. Intermittently it will turn off but always seems to come back. One major issue I have noticed is when I start the carup after sitting for a long period of time (Over night/a day later) it the idle will bounce up and down a few times before becoming stable.

Here is a list of things I have done to attempt to fix the issue.

-Replaced MAF sensor
-Replaced upstream O2 sensor (pre cat)
-Tested air intake gaskets and they seem to be sealed up good

Here is a list of things I would like to do but I am not sure if it will fix the issue

-Replace fuel filter
-Clean EGR valve and replace gaskets
-Replace vacuum hoses ( though I am not sure which hoses that would be it was just a recommendation someone gave me)

Any suggestions will be of great help.

-Cheers

You should check for vacuum hose cracks. Bend each at the connector to spot the crack. Also, throw in some Techron injector cleaner into the gas tank.

It's pretty easy to spray some starter fluid around the vacuum hoses to check for leaks. If the idle increases, that hose is cracked.