I know I need to clamp down the air bypass valve, then adjust the screw until the truck is about stall and adjust it till it's running smoothly. Preferably adjusting the base idle with a handheld tachometer until it's 725 rpm....correct? As for turning the screw, is turning clockwise restricting airflow adjustment?

Well, I have a couple of questions on the procedure. When adjusting the idle, does the car need to be fully warmed up? and do I adjust the base idle when the truck is "Park" or "Drive" position?

I've been adjusting the base idle about once every two months and I even purchased a laser handheld tachometer to help with the job. The problem with the tach is that I'm reading off the alternator and the rpm fluctuates, I can't get a steady reading. I seem to be doing better by "guesstimating" with the dash tach.

I took some pics of the current on dash tach rpm readings... Picture #1 is the truck in Drive and it's barely hoovering above the first marker (I'm assuming the first marker is .500 rpm) and picture #2 is the truck in park. When I put the truck into Park, the rpm jumps up to the second marker (I'm assuming .750 rpm) and it whines constantly loud. Do these readings look low or just about right? Thanks.[/align][/align][/align] [/align]

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Are you sure it needs adjustment, could be something else going on with the engine causing the low idle.
As for setting it, do it when the engine is at operating temp, in closed loop and in park.

 

I've cleaned out the stepper motor housing, replaced the stepper motor, checked for vac leaks and replaced cracked hoses, replaced MAF sensor, replaced left bank O2 sensor, replaced plugs and wiresand just recently replaced the alternator. All these items were replaced in the past 2-4 months.

I can't think of anything else that will cause an idle issue. Before changing the alternator, my idle would surge up and down in Drive or Park. When it did surge, it would dip below .500 rpm and hoover around 600ish rpm. The truck would idle roughly and feels like it wants to stall. After changing the alternator, the idle has stablized a lot more and 90% of the time it hoovers slightly over .500 rpm in drive and close to .700 rpm in park (as pictures below). But I left it idling in park yesterday for about 10 minutes and my CEL came on. The truck threw a code 48... which is the stepper motor.

Honestly, I'm stumped... any suggestions on other possible culprits? Thanks.

 

You have been busey, I am going to have to ponder this one, I'll get back to you.