The tube connecting to the fuel pressure regulator diaphragm nipple is a vacuum tube.

After I cleaned the MAF and installed a new air filter, I then cleared the codes; except for the DM (pin 3) code 19 - it would not erase, but the CEL went off and has been off for the past 10 trips. The motor runs good, the same as before this happened.

The only vacuum related issues in the past involved the trans upshift delay so I had that vac line plugged.