Hi!

WRT your front axle, it's only locked if the 4WD light is lit on the dash. I don't think you'd need manual hubs. One side of the front axle is disconnected in 2H, this is all controlled by vacuum.

If you park the truck in a quiet place and open the window, there is still some vac pressure after you stop the engine. You should be able to to hear the thing moving as you shift between 2h and 4h with the ignition on. When there's no vacuum pressure left, 4wd light does not come on, proving that that light's only on when the axle's locked.

So driving in 2H only one of the wheels is connected to the diff; the input and other wheel are free, you should still be able to drive it.

WRT your idle it should idle at 700ish after it's warm with a/c off and no load from things like power steering.

Here's the idle speed procedure from the 97 manual:
IDLE SPEED
INSPECTION
1. INITIAL CONDITIONS
(a) Engine at normal operating temperature
(b) Air cleaner installed
(c) All pipes and hoses of air induction system connected
(d) All accessories switched OFF
(e) All vacuum lines properly connected
HINT:
w/ EGR: All vacuum hoses for EGR system, etc. should be properly connected.
(f) SFI system wiring connectors fully plugged
(g) Ignition timing check correctly
(h) Transmission in neutral position
2. CONNECT TOYOTA HANDûHELD TESTER OR OBD II SCAN TOOL (See page EMû8)
3. INSPECT IDLE SPEED
(a) Race the engine speed at 2,500 rpm for approx. 90 seconds.
(b) Check the idle speed.
Idle speed: 700 ? 50 rpm
If the idle speed is not as specified, check the IAC valve and air intake system.
4. DISCONNECT TOYOTA HANDûHELD TESTER OR OBD II SCAN TOOL

If you want to verify ignition timing it should be at 12.5 to 22 BTDC. With a jumper between TE1 and E1 on the diagnostic connector under the engine, it will shift to 8-12 BTDC, at 700 rpm idle.