I recently said goodbye to a 2002 Mazda Protege that made it to just over 300,000 miles. So naturally I purchased another Mazda - 2007 Mazda6, 5-speed manual, 91k miles.

Besides the difference in shifting feel being night-and-day, I've noticed that as I'm accelerating and upshifting, the RPMs don't drop immediately when I release the clutch, even when I'm entirely off the gas pedal. There is nearly a full second delay from clutch release until the RPMs begin to drop, leading to a significant pause between gears as I wait for my revs to match my desired gear.

Is this normal, or could my hydraulic system be acting up?

  • @Shamtam Thanks, I think that's it. After another few months of driving with it, I've noticed that if I back off the gas a little more than I am accustomed to before releasing the clutch, it behaves more like I would expect it to and it's easier to hit my desired RPMs. – Dan A. Dec 24 '15 at 21:25
  • Changed my comment to an answer! – Shamtam Dec 25 '15 at 16:40

This is Rev hang. It releases less emissions than a standard manual gearshift.

Modern car manufacturers have strict emissions guidelines to meet and in a manual transmission the ECU has less control of the engine and thus less control of emissions released.

Keeping the throttle open after a gear change allows airflow to the engine to combust all remaining gases in the chamber. This is what the catalytic converter is designed to process, so emissions will be better processed than if we closed the throttle early.

If you're interested I highly recommend Engineering Explained's video where he explains this very well: https://www.youtube.com/watch?v=mm6SSeLivqE

  • 1
    Changing my accepted answer to this. I happened to watch that Engineering Explained video not long after it was posted, and it made so much sense! – Dan A. Nov 17 '20 at 5:34
  • Thanks @DanA :) Me too! I just wanted a chance to share my new knowledge to be honest XD – Jesse Reza Khorasanee Nov 17 '20 at 23:03

Could very well just be a heavier flywheel on the newer car (which leads to more rotational inertia causing the engine to take longer to rev down with no power applied). Sounds normal to me.

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