P0171 & P0174 Lean Codes
 

I struggled to resolve this issue on my 2003 Mazda MPV for over a year. I replaced PCV and hose, all o2 sensors, MAF sensor and still no relief. My regular mechanic and my shade tree mechanic were stumped. Then I took it to a reputable well known mechanic here in Arizona who ran an diagnostic test ($75) and pin pointed it immediately. Something I never would have checked (and quite frankly never heard of): It was the "Intake Runner Control Actuator Seal". Total cost for everything: $245.00. All is well now!

Yeah whenever you have lean burn codes you can test that by spraying VERY carefully around your intake and anything that looks like a vac hose with either (starting fluid), if you hit the leak area the RPMs should pick up a bit with the extra fuel, I did this to find my friends intake leak on his old BMW 3, ran like crap until I hit the runner with the bad seal, ran great for that second. Just be careful around the exhaust bits, that can ruin your day in a hurry! Did they have to replace the actuator or could they get to the seal?

I found a leak in the brake booster by using that technique. They just had to replace the seal.