'92 1.6 fluctuating idle with Idle valve plugged in - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-20-2011, 08:33 AM   #1
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Default '92 1.6 fluctuating idle with Idle valve plugged in

I've got my car to idle on the MS at a steady 950-960rpm but im struggling in getting it to idle with the valve plugged in.

Without the valve plugged in it will hold a steady idle a 950-960rpm. When i plug the valve back in though the idle will fluctuate between 900 and 1100rpm every 2-3 seconds after coming to a stop or touching the throttle.

The valve settings im using are below as recommended by reverant:



Also attached a short datalog i did. It starts with the valve plugged in and then you can see the idle becomes steady when i unplug the valve.

Any suggestions on what might be causing the unstable idle?
Attached Files
File Type: msl idle log.msl (481.9 KB, 73 views)

Last edited by Valentinik; 02-20-2011 at 08:35 AM. Reason: Corrected information
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Old 02-20-2011, 08:39 AM   #2
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I'm on my iPhone so can't see the log, but are AFRs steady? If not that'll cause idle instability, as will if it's too lean.

if the above are good, try reducing I and P until idle is steady.
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Old 02-20-2011, 08:43 AM   #3
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They seem to be quite steady with it unplugged but as soon as i plug the valve in they fluctuate with the idle.
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Old 02-20-2011, 08:54 AM   #4
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Yeah so you need the AFRs to be steady as the rpms are higher/lower it's a very tricky balance I still haven't nailled it.

Set it to open loop and tune the AFRs to be consistent in-between the idle target areas I.e. 900 rpm -1200rpm
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Old 02-20-2011, 12:02 PM   #5
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Too much I.

you need to retune your PID gains settings. try P-10 I-42 D-5.


and your operating the valve at an odd frequency. use 6 for the multiplier.
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Old 02-20-2011, 12:36 PM   #6
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i tried pwm warmup and the afrs were still just as stable as with the valve unplugged, only in closed loop they were fluctuating

I switched back to closed loop and tried brain's settings and it seems to sit around 930-950 which is a lot better. I'l give it a try during the week from a bone cold start but its a huge improvement.

Thanks Braineack
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Old 02-20-2011, 07:30 PM   #7
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There's a guide on Nutz for tuning PID as is there one in the MS manual

Both would be worth a good read
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