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Old 05-31-2007, 11:22 AM   #1
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Default Hot restart, rubbish idle

I posted this on MSextra, but have had no response..

What settings do I need to alter to improve my idle from a hot/warm restart

I think it's a heat-soak issue more than anything as the Idle returns to normal after less than 1/2 mile of driving.

I guess it's to do with coolant related air density? any tips for tuning that section??

Also, this may or may not be related, but from a cold start my idle is fine, i.e. it sits at 1500rpm (where I've set it at). I drive off and 5-10 mins later the engine is warm, yet the idle is at 1800rpm, and the IdleDC is at 0. 15-20 minutes of driving later i.e. heat soaked the Idle is back to it's 900rpm set-point and the IdleDC is around 10

Thanks peeps!
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Old 05-31-2007, 11:30 AM   #2
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the second issue may be a vac leak that could be a vacuum tube expanding at certain temps and then re-sealing at higher...? easy enough to know if it's the ISC by unplugging it when it goes to 1800. Also check your throttle stop to make sure it's not propping the throttle plate open.

Since you have an LC-1, you can monitor your AFR during idle and warm up. I think a 13.5:1 AFR below 60C coolant temps is a decent place to start... if CLT is above 60 then hot restart AFR should probably be between 13.8 and 14:1 though my car is fine at 14.3-14.6.

what does your idle do prior to settling down when you hot restart?
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Old 05-31-2007, 12:42 PM   #3
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Quote:
Originally Posted by y8s View Post
the second issue may be a vac leak that could be a vacuum tube expanding at certain temps and then re-sealing at higher...? easy enough to know if it's the ISC by unplugging it when it goes to 1800. Also check your throttle stop to make sure it's not propping the throttle plate open.

Since you have an LC-1, you can monitor your AFR during idle and warm up. I think a 13.5:1 AFR below 60C coolant temps is a decent place to start... if CLT is above 60 then hot restart AFR should probably be between 13.8 and 14:1 though my car is fine at 14.3-14.6.

what does your idle do prior to settling down when you hot restart?
not thought about a vacuum leak only when heatsoaked, will check that out.

Throttle stop is a'okay I just recently looked at it.

Idle when heatsoaked/hotstarted is waaaay low around 450-500 rpm
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Old 05-31-2007, 12:53 PM   #4
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actually this sounds more like an ISC issue than a fuel issue... if it doesn't die right away or sputter to an idle, the fuel is ok.

but since it's steady and 400 rpm off target, i suspect something else. might be a MS setting but I'm not familiar enough with it. is there a CLT idle speed or AIT idle speed target?
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Old 05-31-2007, 01:10 PM   #5
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what is your warmup compensation set to, and what is your after start enrichment set to? Could you be bogging the motor with to much fuel, what is your idle afr and afr when these stumbles happen? I recently found a leak in one of my injector o-rings that screwed all my maps up. What about your idle bypass actuator could it be adding tension to your belt making the super harder to spin? i hope this helps
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Old 05-31-2007, 02:00 PM   #6
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There's Idle advance, IAT/CLT related ignition, coolant related air-density, after start enrichments, and the warmup wizard....
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Old 05-31-2007, 05:01 PM   #7
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Quote:
Originally Posted by magnamx-5 View Post
what is your warmup compensation set to, and what is your after start enrichment set to? Could you be bogging the motor with to much fuel, what is your idle afr and afr when these stumbles happen? I recently found a leak in one of my injector o-rings that screwed all my maps up. What about your idle bypass actuator could it be adding tension to your belt making the super harder to spin? i hope this helps
I don't think it's anything to do with the idle bypass, as it was like this prior to the charger install - but good shout that!

AFR's are generally where I want them when the idle is too high, warmup compensation could be a go-er I'm pretty sure that needs work tbo.

Afterstart enrichment only activates for 10 secs after starting so it's not that

Ta for the ideas, I'll dig deeper!
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Old 05-31-2007, 06:47 PM   #8
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the only thing that can raise idle speed that I'm aware of is AIR. more air. find out how it's getting in and you'll find your problem.
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Old 05-31-2007, 06:49 PM   #9
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for hot restart, your IAT sensor is heatsoaked and MS pulls fuel. You are right, change the coolant temp related air density ... in other words make it more than 100% for large CLT values.
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