RPM Drop At Idle From Fan - Mustang Evolution

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Old 03-24-2015, 09:41 PM   #1
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RPM Drop At Idle From Fan

Hello,

I have a 2003 V6 mustang convertible. After my car is warmed up and the radiator fan turns on the rpm's drop to under 500 and the car shakes as if it will die then it jumps back up then settles back around 750. When the fan comes on again the process starts over.

I have a new alternator (motorcraft), new wires, new plugs, new air and fuel filter, new IAC, new TPS, new EGR and have seafomed and change oil regularly.

When I bouth the car (almost a year ago) it had a dead batter and the guy replaced it with a no name battery... it literally says battery on the sticker... could this be it? I dont think so because it starts fine everytime

Also the ac cause the issue (because the fan is turning on) and using the power windows drops the rpm's also

What can I do to try to fix this? Any Ideas or suggestions is greatly appreciated!
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Old 03-24-2015, 11:13 PM   #2
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Just a shot in the dark here, but could you AC compressor be bad?


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Old 03-24-2015, 11:16 PM   #3
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I do not think it is... It blows cold air and seems to function fine also it happens even when the ac is off and the radiator fan kicks in


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Old 03-24-2015, 11:25 PM   #4
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My first guess would be battery given the new alternator

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Old 03-25-2015, 08:55 AM   #5
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My first guess would be battery given the new alternator

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Correct me if I am wrong because I do not know all that much about cars but.... I thought the battery pretty much just started the car and the alternator was used for electrical needs once the car is running
Like I said I don't know this just kind of what I thought


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Old 03-25-2015, 10:22 AM   #6
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Originally Posted by rodgersc77 View Post
Hello,



I have a 2003 V6 mustang convertible. After my car is warmed up and the radiator fan turns on the rpm's drop to under 500 and the car shakes as if it will die then it jumps back up then settles back around 750. When the fan comes on again the process starts over.



I have a new alternator (motorcraft), new wires, new plugs, new air and fuel filter, new IAC, new TPS, new EGR and have seafomed and change oil regularly.



When I bouth the car (almost a year ago) it had a dead batter and the guy replaced it with a no name battery... it literally says battery on the sticker... could this be it? I dont think so because it starts fine everytime



Also the ac cause the issue (because the fan is turning on) and using the power windows drops the rpm's also



What can I do to try to fix this? Any Ideas or suggestions is greatly appreciated!

The drop is From the fan taking power from the motor since the alternator request more power via using the serpentine belt so it can power the fan this causes more stress on the motor so you rpms drop for a second. It's the same thing with the ac but you might see a slightly larger dip since more power is being taken for the ac condenser. The rpms come back up since The motor hurries and generates more power so it can balance its self out, to the proper rpm level.


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Old 03-25-2015, 12:48 PM   #7
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The drop is From the fan taking power from the motor since the alternator request more power via using the serpentine belt so it can power the fan this causes more stress on the motor so you rpms drop for a second. It's the same thing with the ac but you might see a slightly larger dip since more power is being taken for the ac condenser. The rpms come back up since The motor hurries and generates more power so it can balance its self out, to the proper rpm level.


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This makes sense... But in other cars I have been in it does not noticeably do this. Is it just normal for the Mustangs and I should not worry about it? Or is there anyway to fix it?
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Old 03-25-2015, 12:53 PM   #8
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This makes sense... But in other cars I have been in it does not noticeably do this. Is it just normal for the Mustangs and I should not worry about it? Or is there anyway to fix it?
Your battery may be too weak. Or just a crappy battery

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Old 03-25-2015, 01:08 PM   #9
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Your battery may be too weak. Or just a crappy battery

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Okay I will probably pick up a new battery then... Any suggestions? Or just go with the motorcraft?
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Old 03-25-2015, 02:05 PM   #10
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This makes sense... But in other cars I have been in it does not noticeably do this. Is it just normal for the Mustangs and I should not worry about it? Or is there anyway to fix it?

It's common on the 3.8 Essex idk why but its truly not a problem to worry about. And I just replaced my battery before winter started as preventive maintenance and it still and probably always will do it. It not even really noticeable! It's only for a couple seconds then it bounces back up! If you like I can take a video of my car doing it!


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Old 03-25-2015, 02:24 PM   #11
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It's common on the 3.8 Essex idk why but its truly not a problem to worry about. And I just replaced my battery before winter started as preventive maintenance and it still and probably always will do it. It not even really noticeable! It's only for a couple seconds then it bounces back up! If you like I can take a video of my car doing it!


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A video might be nice lol. Yeah mine only happens for a few seconds but then a few sends later it happens again. The really annoying part is how feels it will die when the rpm's drop

Thanks through it makes me feel a little better
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