Since you have checked everything and are sure it’s good in the harness and the sensors, I’d grab a junkyard computer for your model year and drivetrain package. I’m not sure what else it could be.
I would assume upstream and down stream, but could surely be wrong.
Well on the tube my sides are broke that hook up to the maf and intake but have lots of black tape around it tho never thought of looking at the bottom will check that out and see thanksYes to the FPR diaphram leaking as being likely problem. If that is not it, look ever so closely at the plastic tube and rubber connectors on tube from MAF to throttle body. I was getting 8 to 9mpg until I found the accordion pleats were worn on bottom of plastic tube where you wouldnt notice the holes. Repaired it and highway mileage went up to 16mpg.
This is a crazy priced part if you buy new, like $150 and newest ones you find in junkyard are like 1994 so going to probably be holey too or at minimum the rubber seals are dryrotted. Cant buy seals separately. I posted a while back how I repaired mine using super glue and baking soda. Should be three pics. I also replaced one end with short length aluminum tube and a generic silicone connector between this tube and the throttle body. You can get these silicone connectors just about any configuration of sizes off ebay, though some come on slow boat from China.
The baking soda sprinkled onto super glue immediately sets it harder than anything you've seen and immediately. Bonds to plastic like nothing else. Lot videos on youtube using this method to repair otherwise impossible to repair plastics. Alternatively some have made a air tube out of pvc drain pipe and fittings. Whatever works for you. I found it was going to cause it to hit hood on my Ranger using round pipe. the OEM plastic tube is flattened into squared oval. So hood doesnt hit it. So far repairs are holding up well.
If you have a leak between the MAF and the throttle body it will cause a low MAF reading. Air leaking in means less air through the filter and MAF and a lower reading. You will get the same effect if the hose from the intake tube to the valve cover is leaking or bad.