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Surging revs, voltage fluctuating, instrument lights dimming

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Am having some strange issues with my 2001 Carrera4.

The car has sat for several weeks, with me starting it for a few minutes every week or two.

Now that I finally am able to drive it, I took her for a mellow ride (as opposed to driving like i stole it)

Everything seemed fine until after a few miles of driving at operating temp, several of the dash warning lights came on.

So, I drove it the few blocks back to my house... the whole time everything felt fine.

Turned the car off, checked fluids, hooked up a meter to battery. Everything looks good.

Minutes later I decided to turn her back on, and I get what is in the video linked below...

RPM is constantly surging, the voltmeter in the dash is going from about 11-11.75, several of the warning lights are on, and the instrument lights that are on will dim with the RPM surges.

After that I have noticed that with the key in the ignition, but with the car off, voltmeter shows about 11/11.5.

Check with my handheld meter on the battery it shows just above 12 volts...

Battery is about 3-4 months old.

Any pointers? I am really jonesin to drive her.

Also I should mention, I am suspicious of the accuracy of my handheld meter... it is a cheap one, and several years old.. though seems correct on my other cars.


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  • Moderators

It looks like you have a failing alternator, or at least a dying voltage regulator. Car should have around14V running and high twelve’s off.

Edited by JFP in PA
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Start by double checking your battery by measuring the specific gravity of each cell and a load test.

If it checks out then you are looking at an alternator or the voltage regulator on the alternator as bad.

BTW... normal charging (engine running) is about 13-14 volts.

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  • 4 weeks later...

For anyone who found this post via searching:

Replacing my alternator did fix the problem... and if you have to change the alternator, you might as well do the belt at the same time.

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