Spawning an expect session within your bash script is typically how you automate interactive prompts.
e.g.
expect -c "
spawn sudo setpci -s 00:02.0 F4.B=00
expect -nocase \"password:\" {send \"$PASS\r\"; interact}
"
Note that this isn't the recommended approach in this case as it is a huge security hole to store your root password in a bash script.
The correct solution would be to edit your /etc/sudoers/
to not prompt you for a password for that binary.
#in /etc/sudoers
neohexane ALL=(ALL) NOPASSWD : /usr/bin/setpci