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RPM Fluctuates while idling and bounces below 500 if revved up a bit

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Old 6/25/06, 02:25 PM   #1
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Unhappy RPM Fluctuates while idling and bounces below 500 if revved up a bit

While stuck in traffic today, i noticed my 06 GT (manual trans) was idling a bit low around 500RPM.

so i tapped the gas pedal, revving it up to 1500 RPM and let go.
RPM then smoothly dropped to around 450, bounced back up to 700, back down to 500, up again to 600 and seemed to stabilize there for a bit.

i left it idling for a while, and noticed the RPM was then continuously fluctuating up and down between 500 and 700!
it certainly is not just the gauge needle. i can feel it.

The AC was on throughout, and i tried switching it off but noticed no difference.

she's in top shape otherwise, and has 10k miles on her, no shudders, vibration, signs of misfire, or error codes on the dash.

now It could be in my head but the only unusual thing i felt was that steering was a bit stiff today, especially when i turn to the left
but since i've been in a minor fender bender (quite literally http://forums.bradbarnett.net/showthread.php?p=679560 ) i figured this might have been reason and set my self to take the car back to the dealer to have the suspension and steering assembly fully checked.
not sure the steering is related, but anything is possible at this point.

i've shot two videos with my phone (low quality/frame rate) showing both symptoms.
- drop below 500 after revving up:
http://www.iihs.net/rpm-issue/drop_below_500.wmv

- fluctuation at idle:
http://www.iihs.net/rpm-issue/idle_fluctuation.wmv

..... any clues as to what may be causing this?
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Old 6/25/06, 03:01 PM   #2
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I get the same thing, but I noticed it with the turn signal on believe it or not. I also notice it with the A/C on when the A/C clutch kicks on & off.
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Old 6/25/06, 06:42 PM   #3
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This happened to me as well. However, it happened after I reflashed the computer with my SCT Excalibrator II/JLT CAI in order to change a setting. I took it to the Ford service center and they reset the computer back to stock and now it is fine. Oh, I also re-installed the stock airbox before I took it in. Now I'm debating whether or not to re-install the JLT CAI with tune. I'm afraid it might happen again.
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Old 6/26/06, 12:14 AM   #4
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Apart from disconnecting the battery for a while, can i reset the computer myself somehow?
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Old 6/26/06, 06:05 AM   #5
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Quote:
Originally Posted by G.T
Apart from disconnecting the battery for a while, can i reset the computer myself somehow?
With my SCT Xcalibrator II, I tried flashing the computer back to stock and disconnecting the battery (both terminals) but the same up and down idle was still there. The service center was able to reset the computer correctly.

Do you have a custom tune installed with a CAI?
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Old 6/26/06, 11:29 AM   #6
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Quote:
Originally Posted by camposl69
Do you have a custom tune installed with a CAI?
nope.. she's bone stock

i just had an idea today that perhaps this is weather related?
Dubai's weather is starting to get ugly, as it soars over 110F with humidity levels around 60-80% on average..
she's been running smooth throughout the "cold" season. so i'm guessing this could be an Air intake issue, where the air isn't rich enough.
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Old 6/26/06, 05:14 PM   #7
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Have you heard about re-learning idle after a battery disconnect?
...but it's on page 205 from the manual...here's a copy of the text...

"Because your vehicle’s engine is electronically controlled by a computer,
some control conditions are maintained by power from the battery. When
the battery is disconnected or a new battery is installed, the engine must
relearn its idle and fuel trim strategy for optimum driveability and
performance. To begin this process:
1. With the vehicle at a complete stop, set the parking brake.
2. Put the gearshift in P (Park) (automatic transmission) or the neutral
position (manual transmission), turn off all accessories and start the
engine.
3. Run the engine until it reaches normal operating temperature.
4. Allow the engine to idle for at least one minute.
5. Turn the A/C on and allow the engine to idle for at least one minute.
6. Drive the vehicle to complete the relearning process.
• The vehicle may need to be driven 10 miles (16 km) or more to
relearn the idle and fuel trim strategy.
• If you do not allow the engine to relearn its idle trim, the idle
quality of your vehicle may be adversely affected until the idle
trim is eventually relearned.
When the battery is disconnected or a new battery installed, the
transmission must relearn its adaptive strategy. As a result of this, the
transmission may shift firmly. This operation is considered normal and
Maintenance and Specifications
205
will not affect function or durability of the transmission. Over time the
adaptive learning process will fully update transmission operation to its
optimum shift feel."
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Old 6/27/06, 12:30 PM   #8
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Thanks for the notes Karman, although since my battery hasn't been disconnected, do they still apply?
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Old 6/28/06, 11:40 PM   #9
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disconnecting the battery and following Karman's tip didn't help either..
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Old 6/30/06, 03:30 PM   #10
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I guess what Camposl69 had the service center do might work or it could be your extreme weather.
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Old 6/30/06, 06:02 PM   #11
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i'm going to the service center tomorrow morning, they said they can take care of it, so now i can only wait and see.

as for the possibility of the weather being the real culprit, i thought so too, but the fact that the problem occurs day and night regardless of the temperature or humidity kinda rules this out.

let's see
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Old 7/6/06, 06:39 AM   #12
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After a week struggling with this issue, it suddenly disappeared!
my service appointment was rescheduled for Saturday the 8th, but i doubt they'd find anything anymore :S

i just hate it when this happens.
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Old 8/6/06, 03:14 PM   #13
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The last checkup yeilded nothing, and the car continued to run smoothly untill early last week when i had my faulty battery replaced under warranty.
now the RPM surging is back, and the technician at the dealership says he'll be checking the throttle body next :S
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Old 8/7/06, 10:50 AM   #14
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I had one instance where the same searching idle thing happened to me last week. It was hot out and my AC was on at the time. I turned it off and it did it for a bit then quit. My car has 11K miles on it now and I have not had the battery disconnected (to my knowledge).
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Old 8/8/06, 09:50 PM   #15
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If nothing else, try looking for a vacuum leak. had a similar problem on my 96 monte carlo and that's what it turned out to be.
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Old 8/11/06, 03:34 AM   #16
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The problem disappeared again.. 1 day before my throttle body check is scheduled! now my car idles smoothly around 800-850, with or without the AC
the RPM never drops below that, and never surges by itself anymore!

it seems like the computer is being reset, then is having a hard time relearning the idle setting!
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Old 8/11/06, 09:42 PM   #17
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have you done the pedal recalibration lately? its easy and seems to cure a lot of ills...really helped mine a bunch.

turn key on- dont start
after some dash lights shut off, slowly smoothly floor it, then release smoothly. turn key off. some say need to repeat a few times.

a couple other guys were having driveability issues and said it made night and day difference too. worth a try
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Old 8/12/06, 05:09 PM   #18
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Read something on another thread, about fuel pumps needing replacing. Don't remember where I saw it, try a search. Sounded like the same problem.
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Old 8/13/06, 04:09 PM   #19
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Quote:
Originally Posted by ford4v429
have you done the pedal recalibration lately? its easy and seems to cure a lot of ills...really helped mine a bunch.

turn key on- dont start
after some dash lights shut off, slowly smoothly floor it, then release smoothly. turn key off. some say need to repeat a few times.

a couple other guys were having driveability issues and said it made night and day difference too. worth a try
Recalibration didn't help at all, i tried it both times i faced this issue.
here's my step-by-step edition for everyone out there:

Reset:
  • With the vehicle at a complete stop, set the parking brake.
  • Put the gearshift in neutral, turn off all accessories.
  • Turn on car without starting the engine.
  • Wait till the dash lights stabilize (some of them will turn off)
  • Step on the gas pedal in one smooth and steady motion
  • Once gas pedal hits the bottom, let go.
  • Turn off car and wait 4-5 seconds.
  • Turn on the engine.
Recalibrate:
  • Run the engine until it reaches normal operating temperature.
  • Allow the engine to idle for at least one minute.
  • Turn the A/C on and allow the engine to idle for at least one minute.
  • Drive the vehicle to complete the relearning process.
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Old 8/14/06, 12:26 PM   #20
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If your car wasn't done yet I'd say go with the fuel pump TSB. My car was running like poo on low gas, and sometimes when it was getting really hot (Canada hot mind you :P). It seems like the bad fuel pump might be starving your car at low engine loads !?
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