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05 ford fiesta supercharger 1.0 revving between shifting

  • guafa
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12 Apr 2019 10:50 - 12 Apr 2019 10:58 #28623 by guafa
Hi everyone,

This one (manual transmission) is revving a little bit up when you press clutch pedal and release throttle pedal (shifting to any gear).This last only 2 sec and then back to idle without hesitation or something else (which makes me think could be normal).

For instance if i rev engine to 1500 rpm, and then shift to second gear, it revs up to 2000 rpm for 2 second and back again to idle.

With no scanner, how do i check whether is or not a factory condition?
Last edit: 12 Apr 2019 10:58 by guafa.

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  • Tyler
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12 Apr 2019 14:59 #28628 by Tyler
Not sure how you'd verify that without a scanner, but I'm fairly sure that's a normal condition. Ford has been using this kind of strategy on their manual transmissions for years, because they assume their customers are clutch monkeys. :silly: The extra revs are there to 'cushion' your next upshift because they figure you're not smart enough to do it yourself.

It annoys crap out of me when I drive one. :angry:

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13 Apr 2019 08:39 #28639 by guafa
Really? That's rare. Thanks

Where i live 70% of vehicles are equiped with manual transmission and only 2 - 3% are Ford.

In case i still want to verify, can i "count" pulses and detect direction of IAC? The point is i don't want to buy a scanner just to connect a ford once a year.

I am assuming that high revs are controlled by IAC.

Throttle body has two blades (let's name them, main blade and bypass blade), they are conected together by a rod) when main blade is completely closed, bypass blade is completely open). Due to both are controlled by your feet, they can't control amount of air once you release throttle pedal. That's why i say air is controlled by IAC.

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13 Apr 2019 10:00 #28642 by Tyler
If it's a two wire IAC, then you might be able to watch the duty cycle on a scope or DMM while shifting. But, that'd also mean getting long enough test leads to go from under the hood into the cabin.

You could drive around with the IAC disconnected and see if it goes away. But like you said, the behavior suggests it's intentional. I'd think a vacuum leak would result in a more consistently high engine speed.

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13 Apr 2019 10:27 #28645 by guafa
Nice suggestion. I gonna do that.

By the way. IAC is a four wires one (bipolar stepper motor)

About vacuum leak. That makes sense. The strange thing is i only have detected when shifting (not in neutral) anyway i'm gonna check in deep. Thanks.

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14 Apr 2019 06:55 #28677 by tmcquinn

Tyler wrote: Not sure how you'd verify that without a scanner, but I'm fairly sure that's a normal condition. Ford has been using this kind of strategy on their manual transmissions for years, because they assume their customers are clutch monkeys. :silly: The extra revs are there to 'cushion' your next upshift because they figure you're not smart enough to do it yourself.

It annoys crap out of me when I drive one. :angry:


I'm an amateur so don't give up on the IAC on my account...

I have a 2018 Subaru WRX and it does this for the reasons Tyler said. When they went to direct injection and gave the computer control of the throttle plate they programmed this 'feature' into the ECU. It is largely hated in the enthusiast community and people pay tuners to make it stop. Anyway, I was thinking you might search for your car and the term 'rev hang'. If it's deliberate you will probably find people complaining about it.

"I'll never know it all but I'm willing to settle for knowing where to find the answer!"

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14 Apr 2019 09:43 #28679 by guafa
Hi tmcquinn,

Rev hang, ok. Thanks

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14 Apr 2019 10:57 #28681 by Tyler

guafa wrote: By the way. IAC is a four wires one (bipolar stepper motor)


Ah that kinda sucks. :silly: For testing, anyway. 'Seeing' what a four wire IAC is doing is kinda confusing on a scope, much less a DMM. There are IAC test kits out there, but they all go in place of the IAC instead of in-line with it. :(

www.amazon.com/OTC-3054E-Noid-Lite-Test/dp/B0071JJYLO

Just thinking out loud here, but if you're inclined to experiment, you could get creative. ;) The PCM is likely looking at the clutch switch position to determine when to do this flare between shifts, right? It'd be tough, but you could try unplugging the clutch switch and using jumper wires to control the input by hand instead. That way, you could control the input yourself, and see if you can reproduce the flare.

OR, unplug the clutch switch after you've started the car, then go drive it.

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Yesterday 13:32 #28816 by guafa
Check this out,

I found an old innova 3130 scan tool which is able to read DTC´s and some live data for this car.

I've found O2 sensor oscillation between 0.24 - 0.8v (never less than 0.24). STFT (+- 3%) LTFT (0%).

TPS at WOT (81%) an always responding inmediately (16%) once i released throttle.

Calc. load (22%) at idle. at WOT (100%). Once i released throttle, went down to 11%, return to 18% and slowly back to 22%

Not vacuum pressure available.

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