Cold Startup Idle Fluctuation - Ford Mustang Forum
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post #1 of 16 (permalink) Old 03-28-2011 Thread Starter
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Cold Startup Idle Fluctuation

On cold startup my daughter’s V6 mustang likes to fluctuate idle speed, up and down, up and down.
We put the Borla S-Type axle back exhaust on her car and noticed it the first morning. I don’t know if it did it with the stock exhaust and we did not here it and the Borla, being so much louder made it noticeable or what but it drives us nuts in the mornings. It seems to go away once the engine is warmed up or is less pronounced. Has anyone else seen or heard this?

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post #2 of 16 (permalink) Old 03-28-2011
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My car doesn't have an aftermarket exhaust, just CAI and tune. However it has always idled up higher (like 1,000-1200 rpm) for 10-60 seconds before coming down to its normal idle rpm. I usually wait until it ends before I go anywhere. I just figure the computer is making adjustments, taking the engine temperature into consideration. I had a race tune on my car before and the idle was always jumping around but we figured out that it was connected to the fan coming on and off.
post #3 of 16 (permalink) Old 03-28-2011
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It's pretty standard for most cars to idle slightly higher on start up to help bring the motor up to operating temperature.

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post #4 of 16 (permalink) Old 03-28-2011
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It's just the O2 sensors not being up to temp, as soon as they get some heat in them the idle will settle down.

No biggie.
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post #5 of 16 (permalink) Old 03-28-2011 Thread Starter
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The high idle is seems fine. The issue is it is just like someone is in the car working the gas pedal between low idle and 1000 RPMs. The engine speeds up then slows down, speeds up then slows down for many minutes, almost like a nice and easy lope.

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post #6 of 16 (permalink) Old 03-28-2011
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I have no clue, does she have a tune? Regardless, the idle should not jump around. Either way I can't believe it would hurt anything to disconect the battery and go through the idle /driveability learn procedures. It may just be it needs refreshing. best regards Plum PS: Real car guys and gals like us, should never read the manual or go to the Dealer. What do they know. All this Internet info is so much better, including mine.........Just thought, compared to your car, I bet your's does'nt do this, and it has a different exhaust.............just saying the daughters car needs some kind of attention.

Last edited by Plumbago; 03-28-2011 at 12:59 PM. Reason: sp
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post #7 of 16 (permalink) Old 03-28-2011 Thread Starter
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Quote:
Originally Posted by Plumbago View Post
I have no clue, does she have a tune? Regardless, the idle should not jump around. Either way I can't believe it would hurt anything to disconect the battery and go through the idle /driveability learn procedures. It may just be it needs refreshing. best regards Plum PS: Real car guys and gals like us, should never read the manual or go to the Dealer. What do they know. All this Internet info is so much better, including mine.........Just thought, compared to your car, I bet your's does'nt do this, and it has a different exhaust.............just saying the daughters car needs some kind of attention.
More knowledge base on the Internet.
BTW, you were a big help!

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post #8 of 16 (permalink) Old 03-31-2011
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Have you resolved this issue yet? best regards Plum
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post #9 of 16 (permalink) Old 03-31-2011 Thread Starter
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Nope.
It either was always there and we did not hear it and the Borla Exhaust now makes it more pronounced or something happened to the car the day we put the Borla exhaust on. The car does have a BAMA tune but the tune was put on days after the issue appeared. Saturday morning I am going to start both cars and see if the RPM gauges are doing the same thing at start up.

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It was always there, mine did it too. I haven't noticed it since I loaded a Tune, but perhaps it has more to do with just putting enough miles on the car, and the computer making some adjustments. Also, the car definitely idles smoother with 91 octane.
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post #11 of 16 (permalink) Old 03-31-2011 Thread Starter
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Quote:
Originally Posted by Joenpb View Post
It was always there, mine did it too. I haven't noticed it since I loaded a Tune, but perhaps it has more to do with just putting enough miles on the car, and the computer making some adjustments. Also, the car definitely idles smoother with 91 octane.
She is running the BAMA 91P and using 93 octang, has 9k miles on it. Mine never did it.

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mine started doing this about 2 weeks ago, no mods at all, 8700 miles. It's not a huge difference, but it hovers around the 1200 rpm range. It has been cool in the morning, but I didn't notice it during the coldest months.
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It is completely normal for your idle to fluctuate after a tune. You need to reset your electronic throttle calibration. Disconnect your battery for at least 30 minutes. Reconnect the battery and start the car but leave it in park with the air condition on for at least 5-10 minutes. Drive it normally for at least 10 miles or so and the computer will recalibrate the idle speed settings. I've done it a few times and it works like a charm. I suggest doing the procedure every time you change a tune.

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post #14 of 16 (permalink) Old 04-01-2011 Thread Starter
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Quote:
Originally Posted by KonaBlueDeuce View Post
It is completely normal for your idle to fluctuate after a tune. You need to reset your electronic throttle calibration. Disconnect your battery for at least 30 minutes. Reconnect the battery and start the car but leave it in park with the air condition on for at least 5-10 minutes. Drive it normally for at least 10 miles or so and the computer will recalibrate the idle speed settings. I've done it a few times and it works like a charm. I suggest doing the procedure every time you change a tune.
Although my daughters car did it before a tune, I will give this a try tomorrow maybe the car needed it before I could hear it.

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My car did it even warmed up after I put the 87s tune on. When I had my new tune made I told Bama about it and they new exactly what I was talking about. The new tune fixed it.

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