Not sure which valve you are talking about, but it sounds like a vacuum check valve. If so, that's easy...air should flow one way and not the other...just blow in both ends to see if you can.
Check motor mounts
it depends what kind of truck it is but most trucks take 5w 20 oil but check the oners manual for specific oil
I'd try a Hane's manual first. It would be the cheapest way to go. As a side note, if there are vacuum lines disconnected, it's possible that it was done to fool an emissions test to get it to pass. If you need to pass another emissions test, you might want to disconnect them again before the test (or spend the thousands of dollars replacing parts trying to get the truck to pass).
It could be the keyswitch or the starter could be wired wrong.
Check battery cables for tightness and corrosion also check solenoid trigger wire
Check under the battery tray.
On a Dodge truck, the vacuum switch is on the transfer case.On a Dodge truck, the vacuum switch is on the transfer case.
check all vacuum lines for leaks
Question is what type of vacuum truck you are looking for. A carpet cleaning vacuum truck or a street level truck to pick up debris in which you will need chemical supplies and such.
locked up or making a growl---remove line leaving comp & check for grey matter --- remove inline orfice to check for metal flakes
Check for vacuum leaks. It sounds like the carb may need to be adjusted.
A vacuum leak in the vacuum assist for the brakes. It is the big round thing that is behind the brake mastercylinder. Check the vacuum connections to this.
It sounds like your truck has a vacuum leak. If the truck cannot build up proper vacuum pressure it will not operate properly.
I would check for a vacuum leak first, then the idle solenoid which is located on the side of the intake plenum.
The blend door could be sticking on the truck. The vacuum system could have a leak. Or the cables to the heat valve could be malfunctioning. Check these three areas to fine why your heater is stuck on hot.
235 Cubic Inch Inline 6.
Check the following...................... 1. A/C heater control doors. 2. Check for vacuum leaks. 3. Check for broken a/c heater doors. 4. Check main controller head.