2003 MPV engine missing
 

My 2003 MPV started missing last week and the check engine light came on. It only missed when I put it in gear and take my foot off the brake, but it runs okay as soon as I give it some gas. I borrowed a code reader and I got P0174, and P0171 as a "pending code". My husband and I were thinking we'd replace the fuel filter, but would it be a waste of time?

That is a mixture balance issue, probably due to an air leak between the MAF behind the air cleaner and the engine. Check the corrugated duct VERY CAREFULLY for splits and leaks, temporary fix with ductape; permanent fix replace duct, under $50. Other than that, improvise a stethoscope and snoop around for air leaks, split tubing, etc. etc.

most of the time its your PCV hose

Check the PCV hose
 

Check between the intake manifold and the fire wall. the PCV hose makes a 90 degree turn at that point and this is where it fails. With your hand you should be able to feel a smooth bump. If it is deformed and sucked in then it need to be replaced.