Nice 4 wheeler, every ranch needs one!
Could be a dirty MAP sensor. They do need cleaned with the appropriate spray occasionally.
May have the wrong plugs in it. Use the brand and part# of the plugs Toyota recommends.
No fancy so called high performance plugs!
AC Delco Iridium where called for, old AC Delco Double Copper where called for, or whatever Toyota calls for, probably a Denso product.
Service the PVC valve or whatever crankcase ventilation system it uses.
Lots of things will cause issues and not throw a code including minor vacuum leaks.