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Old 12-21-2012, 05:53 PM   #1
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Default Frustrating IAC issue..

I'm having somewhat of an interesting IAC control issue...

When i start the car cold everything is fine, the IAC works normally, warm up enrichment etc. are good, but whenI hit about 140* coolant temp, for some reason the IAC duty goes from 34% to 50.8% and locks there(car revs from 1300rpm to 2200 rpm) . At that point if I shuot the car down, and restart it, it works normally, sitting about 27% while driving, 30.1 for clutch in idle down, and idles about 30.1% at 850 rpms. The RPMs will idle dead solid at 850 (+/- 10) BUT I have to shut the car off and restart it warm otherwise the IAC pins at 50.8 and will not move, even while driving ( sucks blowing boosted air right back out the TB - I loose roughly 4psi with the valve sticking open like that...

I only had shadowdash with me today, But, from what i saw, IAC step stays dead set at 130, while IAC duty cycle is 50.8. It actually causes the over run to kick in, so i've got a really annoying high idle... until I restart it.

Any quick ideas that might be causing this issue? ( works normally, and idles great after the "reboot".. it's only coming out of warm up that has the issue)
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Old 12-22-2012, 12:17 PM   #2
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I have experienced similar issues randomly. Every once in a while, the IAC shoots up to around 50% PWM, pushing the idle up to around 2,700 RPM.

Sometimes it only does this for a short period, sometime it just won't quit, at which time recycling the MS solves the problem.

It always does this while in CL Idle, but the high RPM puts it out of CL range, so I don't understand why it keeps the IAC PWM up so high.

Other than this issue, my idle is great.

Looking forward to any input on this.
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Old 12-22-2012, 12:36 PM   #3
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ms1 ms2 ms3?
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Old 12-22-2012, 12:50 PM   #4
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Mine is a DIYPNP.
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Old 12-22-2012, 03:30 PM   #5
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DIYPNP as well. I pulled the board and made sure I didn't have any cold joints, and haven't found any, so I don't think it's on the construction side.

The "normal and correct function " after a reboot is what's got me... I can't for the life of me figure out why it does this as it comes off warm up. It's not ASE, as it won't do it on a warm start, the cranking pulse and everything else is fine.

Once warm it's perfect, from overrun cut it falls to 1100rpm, the IAC duty bumps to 40% (ish), then quickly tapers to the min setting, giving a nice stable idle at 850 rpms.

With A/C turned on at idle it drops to 700rpms, the valv moves to 41%, then settles at 35% giving a stable idle.

It's -only- after a cold start, the car will idle down from 1800 rpm to the warm up curve, the valve closes progressively as the car warms up, and then between 100-130deg coolant temp, the IAC goes to 50.8% duty, iac steps to 130, and it stays there, even when it's bouncing off the over run fuel cut.

I gues turning it off, and on again isn't the end of the world, but it is annoying to say the least
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Old 12-22-2012, 04:37 PM   #6
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What idle algorithm are you using?
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Old 12-22-2012, 04:57 PM   #7
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Pid closed loop. It's a 1995. I wish I had full access to the tune, but don't have my laptop with me.. My valv allies were something like 65 ish open, 24 closed, min duty set at the low value 24. PID were 2,5,2. Tips activation is .8 (clean signal) dash pot 4.3. Pid disable 850 rpms, closed idle target is 800, open 1200.
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Old 12-22-2012, 05:25 PM   #8
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Post msq
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Old 12-22-2012, 05:30 PM   #9
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Quote:
Originally Posted by Braineack View Post
Post msq
I wish I could ! I'm using an old droid x that no longer has a cell plan, connected via Bluetooth.... I think the best I can do is upload it to the shadow tuner studio.

Perhaps if you can tell me what your looking for, value / data point wise I can set it up and grab a screen grab?
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Old 12-22-2012, 05:32 PM   #10
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What are the pid lock out settings?
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Old 12-22-2012, 05:46 PM   #11
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Quote:
Originally Posted by Braineack View Post
What are the pid lock out settings?
I think it was 30rpm/sec and 30kpa... It's indicating CL Idle on shadow dash when it happens though..
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Old 12-22-2012, 05:48 PM   #12
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But... I'll add, the clutch switch ( cruise control) is broken... But I don't have cruise. Launch control, while off, says ready full time
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Old 12-31-2012, 12:05 AM   #13
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Ugh.. problem found.... After I had an issue with a bad burn over bluetooth, I transposed a wierd number into the Min duty for PID that was larger than the valve open setting... when it came off WUE/ASE it went to 50.8 and stuck. Not quite sure why it acted the way it did before...

Idle is great, stable at 870 RPMS, but A/C is still giving me fits, and I've got to dig into the PID settings some more it seems, and / or change the valve open RPM. It seems like it's hitting that vaue and snapping the IAC closed, causing it to drop and stall sometimes, but if I come down to CL idle with the A/C on, it holds 1,000rpms until the clutch cycles then it gets all out of sorts again... It also seems like the vlave isnt moving fast enough, so, prob need to add the mod board and get the frequency clocked up more (with out the hum)...

oh well, another Day. Until then, i just won't turn on the A/C while at idle
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