Re: Is 900rpm too high an idle?
Well, I think I'm pretty much done with this problem:
Finally got the OBD reader setup (a bluetooth ELM327 and a Torque app on my Driod, very cool). Turns out the tach is not too accurate at low RPM readings, and the engine is turning 700, not the indicated 850.
After one cleaning of the dang K&N filter, I'm giving up on those things - - what a huge PITA. I put a Fram in, lots of nice clean white pleats, runs great. Also, the Fram base seal is a LOT better than the skinny, tired old K&N seal; I feel more confident that only clean air is getting into the innards of my engine.
Comment for all on that IAC adjustment screw: I messed with this endlessly, and it has virtually no effect on idle speed at all, nor is it intended to. That screw has only one purpose, and it is to keep the IAC butterfly from contacting the walls of the air passage. If it does contact the walls, it will stick and scuff. The adjustment screw should be set so that the butterfly ALMOST hits the walls, but not quite. You can detect this with a feeler gage, or by "feeling" for the sticky point and turning the screw a quarter-turn past this point.
Another thing about the pesky IAC -- that "coating" they placard for is just plain useless, the IAC gets filthy anyway, and the dirt/grime buildup on the walls of the IAC, over time, will cause the intended bleed-air to be altered. So, like many others, I ignored the "don't clean" warning and got all the gunk out of the IAC, set it up right, and all runs great now, at a reasonable idle RPM.
Bottom line: I learned a lot, found a cool new tool (bluetooth OBD), and got my truck running very nicely. Oh yeah, it looks like I picked up at least 10% or so in mileage too.
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Nearly stock 1996 STX 4.0 automatic
6" lift & 31" tires, 4.11's, snorkel,
locker rear end, aluminum wheels
Lots of light-weight changes (towed behind RV)
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