start/idle problem

My son has a 2000 Silverado with a 5.4 liter V-8 that just started acting strange at start-up. Normally it should fire up and idle without hitting the gas pedal, lately it wants to be difficult starting and once started, the idle is very low until you give it some gas. I've checked the fuel pump pressure and it's got 50 psi, air/gas filters are also okay. There is no check-engine light on either. I'm guessing it's one of those sensors, oxygen or other. Any ideas anyone? Thanks.

Possibly dirty injectors, IAC valve or TB. Another thing that is worth checking is the fule presure regulator.

Possibly dirty injectors, IAC valve or TB. Another thing that is worth checking is the fule presure regulator.

What are the IAC valve and TB? I suppose a mechanic with an engine analyzer can fix this pronto. Could I determine the cause with the Autozone analyzer or would I need something more sophisticated? Also with 50 psi at the Shrader valve, wouldn't this mean the fuel regulator is good? I would think if the pressure was low then a possibility.

Thanks.