In my search trying to figure out what is causing this code, I have done some overdue maintenance. I have cleaned my MAF sensor, changed both O2 sensors, changed fuel filter and my PCV valve. Code is still on. It may just be a vacuum leak I'm unable to find. Would you think it's the intake manifold gasket?

When I changed my pcv valve the hose was dripping oil. (Also started to change my spark plugs but noticed there was oil in the holes). Should I be concerned? It could have been caused by my valve cover that was leaking a few months ago. How can I clean the oil out? Would seafoam work or it is more technical than that?

Truck is 2010 w/ 185k

 

Welcome to the forum

P0171 System too Lean (Bank 1)

4cyl engine just has Bank 1

Lean code means the computer had to open fuel injectors at least 20% longer than it had calculated to balance front(upstream) O2 sensor's voltage
Engine was never running Lean, just FYI, thats not what this code means

Computer "knows" its running a 2.3 LITER engine, so it knows it can suck in 2.3 liters of air every 2 RPMs
It bases its injector open time on this, and then adjusts it using input from MAF sensor and air temp sensor
If there is an "air leak"(vacuum leak) then MAF sensor data won't be correct, because ALL the air is not passing thru it, so it under reports air flow and computer has to add more fuel that it calculated(P0171)

O2 sensors are the only sensors that WILL wear out, 100k miles or 12 years, they use a chemical reaction to detect Oxygen in the exhaust, and the chemical gets used up
And as they wear out they show False Lean, so MPG goes down bit by bit, well worth the money to replace them when they are older, they pay for themselves plus some in best MPG for next 100k miles or 12 years

Computer expects 55psi fuel pressure at the injectors, there is no fuel pressure sensor, so if fuel pressure is low then less fuel flows out of the injectors, so computer has to open injectors longer than it calculated(P0171)


Yes, leaking valve cover will cause oil to be in spark plug holes, use a paper towel or ??? to try and get as much out as you can, then remove spark plug, a little oil won't hurt the cylinders
Might get a puff of smoke on first start up

The clogged PCV Valve hose can also cause a leaking valve cover gasket
All engines generate Blow-by, when a cylinder fires, some of the hot exhaust gas "blow-by" the piston's rings and into the crank case, because the gases are HOT it vaporizes some of the oil coating piston, rings and cylinder walls as it "blows-by", this is where ALL oil vapor in the engine comes from, no other part of the engine gets hot enough to vaporize oil

The blow-by generates positive pressure inside the crankcase and valve cover area(it has open drain holes down to crankcase)
If pressure can't get out then it will force its way out thru oil pan gaskets and valve cover gaskets
PCV system is there to relieve that pressure, it uses engine vacuum to suck out the pressure and any oil vapor so it can be burned in the engine
If PCV Valve or hoses get clogged up, then you get valve cover gasket or oil pan gasket leaks

 

I'm working on the same code but I'll post separately to not hijack your thread. If you're still stumped, check it out.