Adjusting idle speed (RPM) frequency?

Bushnut

First Fill-Up (of many)
so when I bought my truck a little over a year ago it was idling on the slow side. Like 650,700 while in gear and a little faster when in park. Btw 2002 vg33. So I sped it up a little so that it was running at 750 in gear.
Lately its been running 785-940 while in gear. So I slowed it down again. How often should you need to adjust idle speed? Shouldn’t it be set and forget? I always burn premium gas do regular oil changes at 5000km using synthetic Oil 10W30. The only new thing I’ve done is a new oil pan and new heater hoses. I did do a rad flush but what came out as not very dirty.
Any ideas?
 

MnNewb

Test Drive
Without any codes or anything obvious, I would be looking for a possible vacuum leak. I don't know what else would cause it to increase.
 
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