High Idle Above 5mph - Cobalt SS Network

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High Idle Above 5mph

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Old 10-09-2018, 01:18 AM
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High Idle Above 5mph

For awhile now Iíve been absolutely stumped that my cars idle will jump up over normal idle, sometimes to 2 k and do whatever it wants, until I get at or below 6-7 mph, then suddenly it listens to me and idles perfect. Check engine light on and it reads a code about the down stream O2 sensor that I do not have installed. Long tube headers and cold air intake and larger exhaust with no tune. Iíve cleaned out the throttle body, replaced the upstream 02 sensor, cleaned the MAFS with no fix. Car just does what it wants when I push in the clutch or when Iím in neutral as long as Iím over that magical 6 or 7 mph and itís pissing me off.

Any my thoughts guys?
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Old 10-09-2018, 01:33 AM
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My tuner hooked his laptop to it while driving and it read the throttle position opened 20-25% at times my foot was no longer on the throttle. But what blows my mind is the exact mph the car reaches that fixes the high rpm 100% consistently. It makes no sense to me.
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Old 10-09-2018, 08:01 AM
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Which version of the Cobalt do you have? I know I have experienced the phenomenon you describe and in my case it had to do with the tune. I guess it is a side effect of a function designed to improve gas mileage and that is why it is dependent on ground speed. If your case, with no tune, I don't know what could cause that. Potentially has something to do with installing a CAI without a calibration though I can't say for sure. Downstream o2 shouldn't effect the way your car runs, is that the only code?
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Old 10-09-2018, 02:00 PM
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on an ss/sc, thats normal. the ecm is programmed to increase the engine idle just after you start moving, and decrease it as your rolling to a stop. this is done to help smooth the car out in slow speed situations (in traffic) where your at idle with the clutch out in gear. this same feature also stops the throttle body from closing to normal idle when you shift, helping to give a smoother shift.
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Old 10-09-2018, 07:19 PM
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Originally Posted by jdbaugh1 View Post
Which version of the Cobalt do you have? I know I have experienced the phenomenon you describe and in my case it had to do with the tune. I guess it is a side effect of a function designed to improve gas mileage and that is why it is dependent on ground speed. If your case, with no tune, I don't know what could cause that. Potentially has something to do with installing a CAI without a calibration though I can't say for sure. Downstream o2 shouldn't effect the way your car runs, is that the only code?
only the code for the down stream O2 sensors. Witch doesnít bother me because I know the O2 downstream is mainly monitoring the cats performance.
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Old 10-09-2018, 07:24 PM
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Originally Posted by Sharkey View Post
on an ss/sc, thats normal. the ecm is programmed to increase the engine idle just after you start moving, and decrease it as your rolling to a stop. this is done to help smooth the car out in slow speed situations (in traffic) where your at idle with the clutch out in gear. this same feature also stops the throttle body from closing to normal idle when you shift, helping to give a smoother shift.
Well, if thatís so, can it be tuned out? Just curious because itís so high idle when I down shift the car wants to keep running that speed. I hear a ton of header pop, witch sounds great, but I can hear the car start to decelerate then the ecu starts adding more fuel so it stops deceleration, then the rule is cut and you hear header pop again etc.. itís just the most annoying feature if it is indeed a feature. Anyone else have experience with this and is it tuneable?
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Old 10-09-2018, 07:43 PM
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Originally Posted by jdbaugh1 View Post
Which version of the Cobalt do you have? I know I have experienced the phenomenon you describe and in my case it had to do with the tune. I guess it is a side effect of a function designed to improve gas mileage and that is why it is dependent on ground speed. If your case, with no tune, I don't know what could cause that. Potentially has something to do with installing a CAI without a calibration though I can't say for sure. Downstream o2 shouldn't effect the way your car runs, is that the only code?
Its an 06 SS/SC to answer your question brother
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Old 10-09-2018, 08:09 PM
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you cant tune that feature out of our ecm, hp tuners never unlocked those things in the coding. other gm computers have the settings for it that can be adjusted.

is your car tuned? you can change the decel fuel cutoff settings.
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Old 10-09-2018, 08:13 PM
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Originally Posted by Sharkey View Post
you cant tune that feature out of our ecm, hp tuners never unlocked those things in the coding. other gm computers have the settings for it that can be adjusted.

is your car tuned? you can change the decel fuel cutoff settings.
My car is not tuned Starkey. I have an HP Tuner on standby waiting to here some advise from this form because heís not sure how to approach this situation. He doesnít do to many drive by wire cars so heís lacking the experience in this cobalt realm. Do you think I have to go to a GM dealer to fix this problem or do you think trimming the decel fuel cut off with HP Tuner would fix the issue here?
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Old 10-09-2018, 08:24 PM
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Originally Posted by Sharkey View Post
you cant tune that feature out of our ecm, hp tuners never unlocked those things in the coding. other gm computers have the settings for it that can be adjusted.

is your car tuned? you can change the decel fuel cutoff settings.
Is the decel full cut off available in HP Tuners for the cobalt? My concern is in most cases the throttle is shown at 20% even when my foot isnít on the gas, and if we trim fule in those cases then Iím sacrificing accelerating performance and that not a good trade off. Thoughts 🤔
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