P0171 keeps coming back
 

A few months ago my 4.2L V-6 2003 Ford F150 had the check engine light come on. Checked the codes and it was both a P0171 and P0174. Checked some forums and decided to take the truck to a mechanic to have a smoke test done to see if there were any vacuum leaks. During the test smoke came out of the EGR valve, PCV Valve and intake manifold gaskets. I personally replaced both of the valves as they were fairly simple to do but I had the mechanic replace the intake manfold gaskets last week.

The mechanic said once they got everything put back together with the new gaskets they had a difficult time starting the vehicle and in the process of getting it to start the spark plugs were damaged by too much gas in the engine so they replaced the spark plugs as well (at no cost to me). I forget why they said they had to do this but they also drained and replaced the coolant and did an oil change as well (also at no cost to me since it wasn't originally quoted as part of the job).

When I picked up the vehicle it started and ran fine and the check engine light was off. Since then I have noticed that if I start the car in the morning to go to work it has to work harder than I remember it working to start but once it starts it's fine. If I have it running, turn it off and then restart the engine, everything starts and runs perfectly. Also, if I go to work and start the card 8 hours later to go home the engine starts and runs fine, no problems. On top of this, it has taken a week and a half but the check engine light has returned with a P0171 code.

What should I check next? The mechanic did not redo the smoke test after all the parts were replaced so I am inclined to redo this since it's only $30 but assuming they don't find any leaks what should I check next?

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