RPM drops when coming to a stop

Tiny
SOLRAC6262
  • MEMBER
  • 2014 PORSCHE PANAMERA
  • 3.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 13,000 MILES
Hello,

when coming to a complete stop RPM drops and causes a vibration for 1-2 seconds and then RPM goes back up again.
same thing happens when I turn the steering wheel side ways, rpm drops and picks back up again
engine sounds like its putting more load.
when windows are rolled up and I press the switch to rolled them up you can also noticed the rpm drop and with other electronicos I noticed the engine note having load, similar as when the A/C in older cars was turned on.
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Thursday, December 3rd, 2015 AT 6:23 AM

9 Replies

Tiny
HMAC300
  • EXPERT
Make sure battery connections are tight and clean and belt to alternator is in good condition recommended replacement of belt and tensioner is 60,000 mi. Clean throttle plate on both sides and iac hole if one with choke cleaner.
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Thursday, December 3rd, 2015 AT 6:54 AM
Tiny
SOLRAC6262
  • MEMBER
I did clean the throttle plate, the battery connections look brand new, but I went to a couple of Auto zone places and they told me that the alternator had failed, one time a guy told me the alternator took him 3 test until it come up good, because it was very slow increasing amp or voltage not sure.

Dealer told me that everything is checking good, I guess they only get it tested with the diagnostic Software.

Thanks for the answer btw

Carlos
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Thursday, December 3rd, 2015 AT 7:30 AM
Tiny
HMAC300
  • EXPERT
Even though connections look brand new they can be corroded where they connect to posts also check ground from battery to body and to engine.
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Thursday, December 3rd, 2015 AT 7:55 AM
Tiny
SOLRAC6262
  • MEMBER
I have the car at the Stealer, also my RpM needle when acceleration before changing gear it was making a quick jump and then doing the gear change.

The guys there think it can be a bad Tach, they think about the dropping of the idle to be normal, I don't think thats normal, but also don't think it can be related to a bad tach as I can hear the engine note changing everytime rpm drops as if I was turning my A/C on and was getting more engine load.

I asked them about the charging system but they keep saying everything is within specs.

I've know a faulty battery or alternator will do crazy stuff, but what about if its starting to fail, but still working, does this sound like something electric is failing?

Thanks again
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Thursday, December 3rd, 2015 AT 4:43 PM
Tiny
HMAC300
  • EXPERT
If it were anything it would be like a charging problem or something like that. I doubt the battery will fail although it's not impossible. You can always get it tested for free at an auto parts to put your mind at ease. That would check charging if car were running as well. Because it's still under warranty not a lot can be done and you have to believe the dealer. About the only thing I've seen on tsb's is using different types of fuel like regular one time premium the next. Try a midgrade for a while and see if it kind of cures it then have them check belt tension with a tensioner gauge, course they may not know what that is either. I don't think anything electrical is ready to fail however. They may be right as well and idle will drop on it, long as it keeps running it may be ok.
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Friday, December 4th, 2015 AT 7:45 AM
Tiny
SOLRAC6262
  • MEMBER
Thank you for your fast response,

sorry to bother you
I was told that the jump on the needle when driving was because of a faulty tach.

Regarding the drop of rpms I was there today to show the technician what I was feeling, the car feels rough, as soon as the rpms increases it feels smooth but also the engine note get rough when I put load like, steering wheel, heated seats or windows, technician did noticed that.

I did pointed out. The first time I noticed the electric was one day I left the ignition on and the a/c running for 15-20 sec and I got a light for battery discharged.

Then I went to NTB checked the battery and told me it was ok but at 60% charge. It was low
autozone tested. I was told the alternator was taking a lot to put charge and it was slowly building up not constant
different auto zone, told me the starter
oreilly auto parts: I was told also alternator had failed the test
oreilly different. Also battery

dealer just told me they checked and everything pass as normal.

Thanks again

sorry if I've been taking your time

Carlos
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Friday, December 4th, 2015 AT 7:57 AM
Tiny
HMAC300
  • EXPERT
Bad batteries will cause all kinds of screwy problems like alternator not charging etc. Check for a vacuum leak and you may want to try a new battery. Vacuum leak like a hose off or broken etc.
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Friday, December 4th, 2015 AT 8:23 AM
Tiny
SOLRAC6262
  • MEMBER
I'll do that as soon as I get my car back from Porsche,

but they always tell me vacuum leaks are imposible as this will cause a CEL I know hard to believe.

Thanks again for your help
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Friday, December 4th, 2015 AT 8:41 AM
Tiny
HMAC300
  • EXPERT
Vacuum leaks can be small and the computer richens the fuel mix to cover it. So it should be checked especially if it may run rough cold then when warm it goes away.
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Friday, December 4th, 2015 AT 12:20 PM

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