Whats normal? | AEM
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boostedj30
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Whats normal?

My question is, whats an acceptable RPM fluctuation in idle?

I am just dialing in my idle.  I have my AFR's at a conservative 13.0, I have adjusted all  my target rpms in the Idle% vs Target graph to keep my rpms matching the target-as close as possible. (Which is 900 rpm's warm engine.) My Idle learned value is + or - 1. My idle error duty is at zero.  

 I set my Idle FB Rate at 500, from the preset 200 and it got me this steady. (it stopped helping from 400 up)  My Idle FB Min and Max are at -15 and 15. 

Im running Injector Clinic 775cc's, and my Battery offset table is matched to the injectors. 

My RPM fluctuates approx 100rpm....is this normal? Anything else to try?  Or am I being to fussy? 

 

 

AEM_GN
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Do you have cams in the car?

Do you have cams in the car?

boostedj30
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Stock cams.  Its an all stock

Stock cams.  Its an all stock engine other than Supertech valve springs, and the injectors.

AEM_GN
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Is the 100rpm swing like

Is the 100 RPM swing a +/- 100 from 900 so 800-1000?
Or is it a +/-50 from 900 so 850-950?

boostedj30
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If my target idle is 900, it

If my target idle is 900, it can swing from 850-950.

AEM_NS
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Don't forget that you have an

Don't forget that you have an Idle FB Dead Band.  If you're within those constraints then you won't have any feedback.  You haven't really indicated how often it swings up or down.  Is it oscillating fast enough that it's noticeable or annoying or does it drop from 900 to 850 and stay there for minutes at a time?  If the later, then I'd say you're fine.  BTW we usually suggest having slightly negative idle learned values.  It's typically better that the "base" position be slightly high and have feedback bring it down some (a few percent) versus being too low because you're more likely to stall. 

boostedj30
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Great information, thanks.  I

Great information, thanks.  I'll fiddle with the deadband a bit, maybe narrow it down to a + and - 25?  So it will keep the idle in a tighter area?

 It fluctuates between 850 and 950 less than every second I would say, its almost hunting.  Thats why I went straight for the Idle FB Rate. That helped a bit, but not totally.  

 

Ill also try keeping  my idle learned values slightly negative.  Ill run a few logs and post them as well

Thanks

AEM_NS
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Eh, I don't think trying to

Eh, I don't think trying to force a tighter control is the right way to fix/tune this.  IAC response is generally slow and not fast enough to really keep a tight idle rpm.  You'd just get it close with actual air control and then use the idle igntion trim to tighten it up further.  Do things improve or worsen with a leaner idle AFR?

boostedj30
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I finally had a chance to try

I finally had a chance to try your suggestions. Unfortunately it still isnt quite how Id like it.

 

I've set my deadbands at +25 and -25 just to try, Ill set them back to 50 and -50.  I have gone back over my idle%vsTarget table to get all the learned values just below 0%, about -1.5 to -0.4%.

 

 I have given my Ign vs Idle table a steaper incline:  

I have a log saved, but I dont know how to upload it.

 

Any other suggestions?

boostedj30
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My log:   http://www

My log:   http://www.filedropper.com/idlepclog

hope it works