I have a 94 4Runner its new to me, 241K on the clock, the air filter has been replaced the oil just changed by PO. I noticed while in line for at a drive-thru that about every 45 seconds there is a slight fluctuation in the idle, by looking at the gauge, i have the idle set at 750 (per tach), it will drop to as low as 500rpms and then go back to 750. The AC was on so i thought it was that, but when the AC was off it would do the same thing but wound drop as much. is this a normal thing? or should i be looking at other things? I figured it was too like clockwork to be fuel, maybe spark? Timing? Or maybe clogged injectors? The truck runs fine, never feels like its gonna die, just a little shaky when it drops RPMs, but then evens out. I wanted to get suggestions before just throwing parts at it. My idle is set at 750, is that too low? any suggestions would be greatly appreciated, I am about 5300 feet above sea level and i only put the cheapest fuel as this is my around town vehicle. Thanks in advance!