# How much idle fluctuation is acceptable?



## jessebruffett (Apr 16, 2015)

2003 Altima 2.5s, 130k miles 5spd.

After some painstaking examinations and diagnostics on top of the purchase of a live stream obd2 scanner, a trip to the stealership I have concluded that the throttle body issue I thought I had is probably normal operation. Except for one thing, with the scanner I have discovered my idle fluctuates between 675 and 725 rpms. Not surging or oscillating but will occasionally drop to 675 and stay there unless the throttle is touched and other times will rest at 725. This doesn't seem like a lot but I've never own a completely computerized car before. So is the variance in RPMS something to worry about since the low end is technically out of spec?


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## jdg (Aug 27, 2009)

Is the RPM actually changing that much? Or is a limitation of your OBD scanner?
Meaning that the scanner's output is in increments of 25 RPM. Call it a "round off" error for lack of a better phrase.
Maybe the RPM is actually only changing by 25 RPM total...low of 688, high of 713. But when it gets down to 688, it rounds down to the next 25, 675. And when it gets up to 713, it rounds up to the next 25, 725.
25 RPM could easily be the difference in a single step in the throttle body or idle air control motor (whatever this vehicle has for controlling idle), as it's not really a 100% precise operation in the first place.
Then you've gotta throw engine loads in on top of that...alternator/battery charging, O2 sensor cycling/fluctuations (slower than a set of brand new O2 sensors but still good enough to function), A/C compressor kicking in and out, blower motors going on and off (automatic climate control stuff), etc.
Sure, the idle should probably be a bit tighter controlled than 25 RPM, but you gotta figure you've got 130K on it. Things are gonna wear, but not be necessarily worn out.


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## jessebruffett (Apr 16, 2015)

I'm using a bluedriver obd2 adaptor to the bluedriver app for my phone. It's accurate to the extent the ECU is. I would think that it's not a terrible thing for it to drop there, it doesn't stall or shutter. Like I said its my first completely electronically controlled car so I wasn't sure how much to worry. I know all the sensors, save the crank sensor, are the original stock ones, but according to the tool they are all operating and reporting writhing standard ranges. As far as I've been able to find specs for them.


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## jdg (Aug 27, 2009)

Sure, all of the sensors are likely all operating at spec's or at least within tolerances, but that doesn't mean that all of those tolerances can't add up in the wrong direction... Slow, older O2 sensor responses, MAF a bit dirty, cam/crank sensor output not what it used to be, a bit of air leakage here and there, rings not sealing like they used to when it was new. It'll all add up eventually.
I say let it ride until something stupid goes on with it. (e.g. stalling, hesitation, etc.)


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## cj1 (Oct 21, 2014)

If you wanted to play with a bit, clean TB and reset/relearn.


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## jessebruffett (Apr 16, 2015)

Did that already a couple weeks ago. But thanks for the advice


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