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Discussion Starter · #1 ·
Hello,
I have a question about my 2006 F-250 PSD. It is stock with 69K miles on it. Every so often at a stop light my tachometer fluctuates a little bit. It seems to rev up some then back down. It will not do it all the time. I have had it in to the dealership 6 times in the last week and the truck is throwing no codes. It will not do this all the time and more so when it is in drive sitting at a stop light. Any ideas? I was told to try a different source of fuel. I have been using Shell with Motorcraft PM-17-A additive since the truck was new.
I have had the newest FICM put on (2 weeks ago) and this has been going on for about 2 months. No excessive black smoke, no loss of power. Any ideas?
 

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Is it doing it idling at a stoplight or just idling parked for a few minutes.

Part of the new flash. Cycles the VGT and a few other things as long as its in park
 

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Discussion Starter · #3 ·
It will do this while sitting at a stoplight or while the vehicle is in drive. When the truck is in park, it idles fine.
 

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A clutch fan that is cycleing to rapidly can cause similar symptoms, it may be that, when the clutch fan locks up it puts a small load on the engine that is noticeable when stopped or parked.
 

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Discussion Starter · #5 ·
So is this something that I can check for and how would I?
 

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Does it do it when the engine is still cold? Like Dave said it's part of the new flash and it's supposed to help bring the engine up to operating temps
 

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Discussion Starter · #7 ·
Yes, it does it when it is cold. I don't understand (sorry) how idleing an engine up and down would help it reach operating temperature sooner.
 

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From how I understand it, it acts like a "high idle" which puts the engine under a "load" causing it work a little bit harder, which in return brings up the temperatures. Instead of it being a true high idle where it'll idle up to 1k and stay there until you hit the brake or turn it off, it goes up and down until the engine is at operating temps. I don't know if it was to help with saving fuel, if the up and down is to reduce wear, etc.
 

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Discussion Starter · #9 ·
It was doing this before the dealership changed the FICM. This was the reason they changed it. Is it possible I had the flash before (when it was in for routine maintenance)?
 

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It could be possible. I don't know how long Ford has had the high/low idle in their flashes. I ran the flash the truck came with (whatever it was in January of 06 which didn't have the up/down idle) until the beginning of April of this year when my FICM and injectors were replaced. That's when I got the flash that has the idle up/down.

Maybe some one will chime in who has had this flash before April to help.
 

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Does your engine actually increase RPM or is it only the tach?

If the engine actually is then I haven't a clue right now.

if it's the tach then try to clean up some grounds and make sure the batteries are hooked up tight.
 

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Discussion Starter · #12 ·
No, the engine actually increases RPM and decreases. Kind of like a flutter. Now the thing hasn't done it all day and I burned out a complete tank of fuel. I just changed places where I have been buying fuel and will see what happens. I am still looking for input. I have a feeling this thing is gonna burn me when I least expect it.
 

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This is how my '04 is performing right now... did you ever narrow down the cause. I don't think its the reflash that is causing it. It could be quite dangerous if your parked to close to someone an it bumps the rpm's right up and you could hit them. Its quite random though, yesterday it did it a couple times and then today it's been fine so far.
 

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For now it is fine, turned out to be the wiring harness going to the FICM. Either loose or a bad connection. No surging for a couple months now ::knock on wood::
 

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weird man. My truck did this same bull**** twice in a 1 month time frame and I never could duplicate it when I was near work. Had the FICM out when I did standpipes and dummy plugs and it hasn't done it since. i do have one tab broken on a ficm harness connector
 

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Yep, thats the best thing about electrical gremlins, they never come out when you want them to. It was could've been the harness that was loose and then you tightened when you reinstalled the ficm.
 
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