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  #16  
Old 12-31-2011, 09:01 AM
groundedracer groundedracer is offline
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Default Re: Is 900rpm too high an idle?

Mine idles at 1200 lol I cannot figure it out everything looks good and everything was cleaned(t-body, maf) screw is all the way out. I dont ever drive mine so I have not worried about it yet. mine is a 4.0 ohv 98
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  #17  
Old 01-01-2012, 10:04 AM
illesg illesg is offline
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Default 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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  #18  
Old 01-01-2012, 01:36 PM
TerrenceStuart TerrenceStuart is offline
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Default Re: Is 900rpm too high an idle?

Quote:
Originally Posted by groundedracer View Post
Mine idles at 1200 lol I cannot figure it out everything looks good and everything was cleaned(t-body, maf) screw is all the way out. I dont ever drive mine so I have not worried about it yet. mine is a 4.0 ohv 98
1200?? you should be going about 45 MPH at 1200. at 65, my RPMs are only at 2000.
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  #19  
Old 01-02-2012, 08:25 AM
groundedracer groundedracer is offline
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Default Re: Is 900rpm too high an idle?

Any idea what I can try? I have a company truck so I don't use it much but would like it to run better when I do use it. I mean it runs great, kinda slow but I think that is just me, and idles real high. I hooked my laptop to it I have live data on it and it says on there it idles at 1200 too. I do not have any codes at all though. I cleaned the MAF, throttle body, and the iac valve with no luck. On start up it idles at 1500 for a few minutes and settles to 1200. I bought it used but from the original owner that worked at the dealership, and he had all reciepts for everything. It has 116k on it. I have owned it for a little over a month have only driven it twice though.
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  #20  
Old 01-02-2012, 10:41 AM
illesg illesg is offline
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Default Re: Is 900rpm too high an idle?

For that high 1200rpm idle, my experience suggests that you have an air/vacuum leak somewhere. Check every vacuum hose you can find, and keep searching, there's a bunch of them. I found my own major leak after about 3 searches, because it was hidden under the IAC. Also be sure that the IAC screw is not too far in (open).

As for the comment about 45mph at 1200rpm, yeah but only if you have enough throttle to supply the needed horsepower. Idle doesn't provide enough power to get the truck up to 45mph. But it sure does creep at the stoplights....
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locker rear end, aluminum wheels
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  #21  
Old 01-02-2012, 12:27 PM
StxDangerRanger StxDangerRanger is offline
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Default Re: Is 900rpm too high an idle?

For the record, Desired idle is somewhere around 750 RPM.
If your idle is at 1200, you have a vacuum leak, luckily for you almost all the vacuum lines are visible on the OHV. If you can't feel or see one, you can do the smoke test. Which pretty much means you hold something that smokes near vacuum lines and if the smoke gets drawn in, you've found your leak.
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  #22  
Old 01-02-2012, 04:09 PM
groundedracer groundedracer is offline
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Default Re: Is 900rpm too high an idle?

Ok,
thanks. I will give it a try tomorrow.
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