Is the coder reader able to connect to the computer?
You should have some codes even if they are not current codes on a '98.
Mentioning this because you could have a computer issue not a vacuum leak.
That would account for lack of power, high idle and flashing 4WD lights.
I would unplug the MAF sensor and start engine, you should get a CEL fairly fast, MAF is a main sensor, just to see if computer and CEL are working as they should.
For vacuum leaks, first you eliminate any leaking hoses by unplugging each hose, one at a time, with engine idling, and plugging that intake port with your finger, if RPMs change then that hose or it's vacuum device is leaking.
After checking all hoses, wait for engine to be stone cold.
You can use ether(quick start) or soapy water in a spray bottle, set it for tight spray pattern
Loosen fan belt and remove it from Crank pulley, so no fan or accessories will be spinning with engine running.
Start COLD engine, it can run fine without water pump for 2 minutes, but will only take a minute to test for leaks.
Spray around lower intake first, by valve covers, listening for change in RPMs
Then move up to upper intake and throttle body