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I've recently found an eco mode on my car that is now showing tips to drive more economically. It's recently flagged up a tip saying 'don't disengage clutch above 1300rpm' which I believe it is showing when I do the following:

When I know i need to be slowing down due to something I've seen up ahead, I sometimes touch the brake to initiate slowing down and then come out of gear by depressing the clutch e.g. from 4th gear (say 40mph, 2000rpm) into neutral and let the car slow down on its own accord, and adjust braking as required based on what is happening ahead. I appreciate the braking distance may increase with this, due to lack of engine braking in neutral gear but is there any harm in doing this? Perhaps by way extra wear to clutch or the transmission, synchros etc?

Thanks

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If you're coming to stop, the inertia of the vehicle drives the wheels. This keeps the engine spinning if you don't touch the clutch until the absolute last moment. In your case it sounds like this is 1300 rpm. Before you press the clutch, the ECU disables all fuel injection for this time period. This saves fuel.

If you press the clutch early, the ECU must inject fuel to cause the engine to idle. Even if the vehicle is moving. This uses fuel, lowering fuel economy. This is why you are getting this tip from your car.

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    Feels counter intuitive hence my above (bad) habit..until this explanation
    – green4rrow
    Oct 4, 2017 at 2:14
  • "If you press the clutch early, the ECU must inject fuel to cause the engine to idle." - could you please elucidate on this? Why disengaging the clutch makes ECU inject fuel? Does "cause engine to idle" mean dropping the rpm to 0? Why does that need to happen? And how does the engine maintain its 1300rpm? Is it using some energy from the drivetrain and movement of the car?
    – Novellizator
    Aug 2, 2020 at 9:26
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    @Novellizator - If you have a new question, please create one. Leaving it here as a comment will not get it the attention it deserves. You can always link back to this question/answer to help in understanding of what you are trying to understand.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Aug 2, 2020 at 15:41

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