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Discussion Starter · #1 ·
Has anyone encountered this? I recently started noticing an issue whenever I drive the ST after a long cold soak (3-4 hrs). RPM elevates by 2-3k everytime I press the clutch, then after a clutch pedal release it slowly bleeds down.
This is really concerning and I am not sure whether this is an issue with the clutch or the pedal or the throttle body or just software in general or something else altogether. The issues goes away in the subsequent trips after the engine is warmed up.
 

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Only thing I can think of is a vacuum leak on the manifold. Once it heats up it seals and the problem goes away.
 

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Discussion Starter · #3 ·
vacuum leak? if the manifold is past the throttle and is leaking, the manifold pressure sensor is going to see that. and if it sees more air than necessary, shouldnt it try to close the throttle more? and if its a manifold leak, why would it just affect the rpm when the clutch is pressed.
 

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vacuum leak? if the manifold is past the throttle and is leaking, the manifold pressure sensor is going to see that. and if it sees more air than necessary, shouldnt it try to close the throttle more? and if its a manifold leak, why would it just affect the rpm when the clutch is pressed.

I know its weird. When ever I have seen something heat related like this I have found it is some type of sealing surface. Also, with a mass air for system the engine like the ST it should reduce speed with a vacuum leak. With speed density it should increase.

Other ideas I was thinking about is maybe it is something to do with the throttle valve. On engines with IAC motors the computer will go to almost zero duty cycle when shifting. It uses the clutch switch as an input. The ST doesn't have an IAC so instead it does it via the throttle actuator. When it gets cold maybe something is binding or there is a lot of carbon build up on the valve causing it to stick open more.

The computer on the ST does also hold the RPM when shifting. It sounds like it is trying to hold the RPM, but something is causing a miscalculated air fuel mixture. I would want to see the fuel trims when this is happening and see if it is in open or closed loop.
 

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Has anyone encountered this? I recently started noticing an issue whenever I drive the ST after a long cold soak (3-4 hrs). RPM elevates by 2-3k everytime I press the clutch, then after a clutch pedal release it slowly bleeds down.
This is really concerning and I am not sure whether this is an issue with the clutch or the pedal or the throttle body or just software in general or something else altogether. The issues goes away in the subsequent trips after the engine is warmed up.
https://www.focusst.org/forum/focus-st-discussions/128706-rpms-actually-increase-clutch-2.html

This sounds similar.
 

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Mine does the same thing recently even on a cold start. I'll be in neutral push the clutch in and RPMs go up maybe 200 RPM. And I hate the Rev hang. It is so annoying.when you go to shift in the RPMs never dropped you have to shift like a grandma.
 

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vacuum leak? if the manifold is past the throttle and is leaking, the manifold pressure sensor is going to see that. and if it sees more air than necessary, shouldnt it try to close the throttle more? and if its a manifold leak, why would it just affect the rpm when the clutch is pressed.
Not sure of the issue, but the reason you may only notice when pressing in the clutch because that relieves the clutch of the tranny load and the flywheel, so it freely spins you don't notice it when the clutch is grabbing because it's holding the cars wieght and trans so it can't freely rev up, that's my thinking.
 

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vacuum leak? if the manifold is past the throttle and is leaking, the manifold pressure sensor is going to see that. and if it sees more air than necessary, shouldnt it try to close the throttle more? and if its a manifold leak, why would it just affect the rpm when the clutch is pressed.[/QU

I know its weird. When ever I have seen something heat related like this I have found it is some type of sealing surface. Also, with a mass air for system the engine like the ST it should reduce speed with a vacuum leak. With speed density it should increase.

Other ideas I was thinking about is maybe it is something to do with the throttle valve. On engines with IAC motors the computer will go to almost zero duty cycle when shifting. It uses the clutch switch as an input. The ST doesn't have an IAC so instead it does it via the throttle actuator. When it gets cold maybe something is binding or there is a lot of carbon build up on the valve causing it to stick open more.

The computer on the ST does also hold the RPM when shifting. It sounds like it is trying to hold the RPM, but something is causing a miscalculated air fuel mixture. I would want to see the fuel trims when this is happening and see if it is in open or closed loop.
The ST is speed density tuned. It doesn't have a mass air flow or MAF sensor. It has map sensors.
 

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There is definitely a MAF on the intake pipe right next to the airbox.
Actually, thats just a temp sensor, but the parts catalogue lists it as a MAP sensor, regardless it is not a MAF sensor. We are speed density, not mass air.
How come you qouted me saying that it's definitely a maf sensor I didn't say that. I said our cars our speed density based tuning, map sensors. But your qoute says my name with an incorrect qoute.
 

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I don't want to look incorrect, I cherish the knowledge I do have. Haha
 

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I'm looking back at the qouting system and I don't know if they need to work on the coding for the site, but they aren't qouting correctly, it's saying qoute from xxxx: but then putting statement from someone else's post, it doesn't seem to qouting the correct info. I see it alot.
 

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I'm looking back at the qouting system and I don't know if they need to work on the coding for the site, but they aren't qouting correctly, it's saying qoute from xxxx: but then putting statement from someone else's post, it doesn't seem to qouting the correct info. I see it alot.
Yeah, i wasnt quoting you. The quote and mention system is on the fritz.
 

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Actually, thats just a temp sensor, but the parts catalogue lists it as a MAP sensor, regardless it is not a MAF sensor. We are speed density, not mass air.
I didn't believe you guys at first. I've never tuned these cars but that sensor where it is and the amount of wires it has said to me that it was a MAF sensor.


Sure enough when I looked at the available data PIDs there was none for MAF.
 

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Actually, thats just a temp sensor, but the parts catalogue lists it as a MAP sensor, regardless it is not a MAF sensor. We are speed density, not mass air.
I didn't believe you guys at first. I've never tuned these cars but that sensor where it is and the amount of wires it has said to me that it was a MAF sensor.


Sure enough when I looked at the available data PIDs there was none for MAF.

I believe they are mapt sensors actually. Speed density and temperature.
 

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I didn't believe you guys at first. I've never tuned these cars but that sensor where it is and the amount of wires it has said to me that it was a MAF sensor.


Sure enough when I looked at the available data PIDs there was none for MAF.
What do we know, only been modifying and wrenching this platform for the last 5 years.

Lmao, just bustin' your balls. The ST is pretty unique in its tuning and what not, it is very similar to the MazdaSpeed3, so besides that, it's a pretty weird machine.
 

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Has anyone encountered this? I recently started noticing an issue whenever I drive the ST after a long cold soak (3-4 hrs). RPM elevates by 2-3k everytime I press the clutch, then after a clutch pedal release it slowly bleeds down.
This is really concerning and I am not sure whether this is an issue with the clutch or the pedal or the throttle body or just software in general or something else altogether. The issues goes away in the subsequent trips after the engine is warmed up.
Did you ever find out the issue? My 2017 focus is doing th same thing
 
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