This is a pic of the harness that I spoke of earlier.
My mechanics explained that if the RPM's ran high or were fluctuating, to giggle this harness and see if any change occurs.
Located in this bunch of wires is one that controls idleing. My Isuzu mechanics have found in a number of Isuzu's that that wire can fray and even ground out.
Granted there are other reasons for an idleing problem that are more common, but here is another possibility.
;Dr;