2000 V6 is running poor or basic maint.

My friend has a 2000 V6 He went at got a plug and wire change, fuel filter, air filter. When all the was changed ran great! but 20-30 mins later sounds like its missing. I gave it some gas in park, and sould like there was a vac. leak. I told him that also need 2 change the pvc valve. Im not sure what else there is. He thinks there is water in the gas or something. I worked on older mustangs but not this new. Any thought or comments would be great!

actually your experience on older mustangs could probably still help a lot. That mustang still has a pushrod motor. Its not as high tech as a lot of new cars.

I highly doubt the egr valve could be the problem, but im sure it wouldn't hurt to clean it.