MT - de-tuned throttle map when clutch is pressed in (disengaged)

[zpower86]

I found an issue with MT Supra's which I wanted to bring to everyone's (any Toyota's) attention. I have not seen anyone discussing this. There are threads about the clutch cdv and clunky shifting, but this topic is a little different.

There is a "Reduced sensitivity" throttle map when the clutch is disengaged (clutch pressed in) versus the normal/baseline throttle map (clutch pedal out). When you have the clutch pressed "In" and slowly lift the pedal, just as you get close to the "Clutch engagement point", the throttle map instantly changes to 'normal' which abruptly increases the RPM/power just prior to the clutch disc catching.

You can test this on any MT vehicle. With the car in neutral, press clutch in, and REV and hold at 2000 rpm, then slowly let clutch out. Your RPMs will shoot up dramatically. The inverse happens if you start with the clutch out. This is repeatable any time, in any gear and in any drive mode for all 2023-2024 MT Supra's.

I think this is a design flaw that needs to be corrected by Toyota for 3 reasons. (1) It makes the car feel clunky during normal up and down shifts since the car adds throttle right at the last second. (2) It is very difficult to set a consistent RPM prior to a launch from zero. This ultimately makes your launches inconsistent in a competitive environment. (3) The throttle blip needed during a heal-toe downshift is insufficient (since the clutch is in). This results in improper/difficult rev matching (when auto rev matching is turned OFF).

Has anyone else identified this problem? Please comment if you have.

Is there any chance Toyota/BMW could fix this on a recall?

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[lucky phil]

I don't believe it's a fault it's designed to be that way. It's an anti stall feature that other cars like the focus RS mk3 have as well. Pretty handy when manoeuvring the car around the garage and tight spaces etc. Just leave your foot off the throttle and gently slip the clutch and creep around. Works well. I'm pretty sure the Supra has it but I'm so used to it on the RS I haven't paid it any attention. I think the Mk3's was more pronounced than the Supra.
The Focus RS also had a stall recovery system so the engine would automatically restart after a stall as soon as the clutch was depressed again. Pretty neat really.

Phil

 

[zpower86]

That’s not what this is. Simply letting the clutch out changes the throttle map, even when the car is in neutral or at speed and in gear. The throttle map should be the same regardless of clutch pedal position.

I don't have a problem with an anti-stall feature. That feature is simply adding throttle when you are not even touching the throttle pedal.

Edited for clarity.

 

[Lonestar_Nomad]

You can let out of the clutch with no throttle and it never bogs down at all. It’s definitely adding some extra fuel during that. Particularly 1st and 2nd. If they want to have a bit of a remap during first, whatever, but that needs to be the end of it. I think Phil is correct as the the reason, but you’re also correct that it’s annoying.

 

[NicKnack]

I always thought downshifting in this car without iMT felt kind of weird and clunky/required way more throttle pedal than seemed normal. All of my other cars are MT and I can crack downshifts off just fine in them but this one always felt a bit clunky.

Thankfully atleast iMT does it really well/has been solid for me so I don't mind leaving it on in this car and just letting the car handle it.

 

[lucky phil]

That’s not what this is. It doesn’t add throttle on its own (if you’re off throttle). It changes the throttle map.

The solution would be to keep the throttle map the same 100% of the time. If it has an anti stall feature that OK too.

What happens if you leave your foot off the throttle in gear, say first and gently release the clutch to the friction point? Do the revs increase slightly at that point.

Phil

 

[Bobby Eccentric]

This explains why merging onto highways is so jerky. I give it full throttle in 2nd, shift at around 5k rpm, smoothly depress clutch and roll back into the throttle at the same time, it sometimes works smoothly, sometimes feels like I am going to break something. It feels unpredictable. But now I know what it is, I can work around it. Thanks OP.

 

[bk5]

I think Phil has it right. This is the iMT give the car some more oomph if you're going to lug the engine.

I have to back my car up a windy, inclined driveway every day to park it in the garage. Which means I am very attuned to the throttle mapping, as it requires a lot of clutch slip to get up my driveway backwards.

And I can say with confidence that there's a stark difference between sport mode throttle and normal throttle. I've tried backing up in normal mode, in an effort to keep exhaust noise lower, but I can't do it; normal mode requires a lot more throttle input and I can't recalibrate my brain quickly enough to cope with it.

So the car is definitely not switching back to normal throttle map if you're in sport and depressing the clutch.

 

[mdpalmer]

Would be helpful to better understand how the system is programmed and what hardware is associated with it. If anyone has access to a system diagram, please share it.

As much as i enjoy driving this car, there are times where I would like to diasble the iMT functions completely.

Anyway I found some documentation from ZF on "clutch systems". Have a look at the clutch by wire and automated manual transmission subtopics. I dont know if any of this hardware is on the Supra.

Anyone who is a tuner or can explore the tuning parameters and tables, please chime in.

 

[Joker328]

Y'all are mucking up the thread/issue talking about iMT and anti-stall. This has nothing to do with iMT (auto rev-matching), as it occurs with that turned off . It's also not about the anti-stall (i.e. automatically opening throttle when lifting clutch even if not pressing accelerator pedal). It's about a change in the throttle mapping when you are feathering both the accelerator pedal and the clutch to either launch the car or shift smoothly.

Assuming what OP described is accurate, this could be another explanation (in addition to the CDV) for why the 1-2 shift is so awkward in this car. The CDV makes it hard to know what the clutch is doing and find the engagement point, while this change in throttle mapping makes it hard to smoothly add in power. I doubt Toyota is going to do anything about either of them, but it would be great if they looked into it.

 

[razorlab]

Very easy to know for sure by logging pedal request and actual throttle position. If the same pedal request changes the actual throttle angle before/after, throttle mapping is changing.

Like this:

FYI, there are different throttle mapping tables for when the car is in Neutral and when it's in gear, which is probably more of what you are feeling.

 

[mdpalmer]

That's really interesting. How did you get access to these tables and can you determine what other parameters influence the actual throttle position specific to an MT car? Thanks for sharing.

EDIT: I see you authored a thread on self tuning with Bootmod3. Sweet.

Very easy to know for sure by logging pedal request and actual throttle position. If the same pedal request changes the actual throttle angle before/after, throttle mapping is changing.

Like this:

FYI, there are different throttle mapping tables for when the car is in Neutral and when it's in gear, which is probably more of what you are feeling.

 

[zpower86]

Y'all are mucking up the thread/issue talking about iMT and anti-stall. This has nothing to do with iMT (auto rev-matching), as it occurs with that turned off . It's also not about the anti-stall (i.e. automatically opening throttle when lifting clutch even if not pressing accelerator pedal). It's about a change in the throttle mapping when you are feathering both the accelerator pedal and the clutch to either launch the car or shift smoothly.

Assuming what OP described is accurate, this could be another explanation (in addition to the CDV) for why the 1-2 shift is so awkward in this car. The CDV makes it hard to know what the clutch is doing and find the engagement point, while this change in throttle mapping makes it hard to smoothly add in power. I doubt Toyota is going to do anything about either of them, but it would be great if they looked into it.

Exactly, thanks Joker328. The issue/complaint I am has nothing to do with an anti-stall or iMT features (those features are good). Additionally, I am not talking about the Sport vs Normal engine mode.

The issue is there is a severely de-tuned throttle map (in any mode) when the clutch pedal is pressed-in.

All MT owners, please go test it. In any gear and any speed (or even in neutral sitting in your driveway), do the following:
(1) press clutch in,
(2) REV and hold at 2000 rpm (or similar),
(3) very slowly let clutch out.
Your RPMs will shoot up dramatically just as you get close to the engagement point.

You can also test the inverse.
(1) clutch out and in neutral
(2) REV and hold at 2000 rpm (or similar),
(3) press clutch in.
Your RPMs will drop down dramatically.

 

[zpower86]

I edited my post #3 for clarity.

 

[razorlab]

Exactly, thanks Joker328. The issue/complaint I am has nothing to do with an anti-stall or iMT features (those features are good). Additionally, I am not talking about the Sport vs Normal engine mode.

The issue is there is a severely de-tuned throttle map (in any mode) when the clutch pedal is pressed-in.

All MT owners, please go test it. In any gear and any speed (or even in neutral sitting in your driveway), do the following:
(1) press clutch in,
(2) REV and hold at 2000 rpm (or similar),
(3) very slowly let clutch out.
Your RPMs will shoot up dramatically just as you get close to the engagement point.

You can also test the inverse.
(1) clutch out and in neutral
(2) REV and hold at 2000 rpm (or similar),
(3) press clutch in.
Your RPMs will drop down dramatically.

Check out the two throttle tables I posted above.

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