Please let me clarify that apart from experiencing my first rev hang in 2003 Fiat Punto in Europe I have not driven recent model Fiat as they are not common cars in Australia.

However, in my automotive consulting business I test drove over 3500 cars in the last 25 years and encountered the feature of rev hang in many recent models. In fact, my last 3 new cars (Toyota Yaris 1.5, Suzuki Vitara and Toyota RAV4 2.4) and other 2 recent model cars (Honda Accord Euro 2.4 and Mazda 3 SP23) also suffered badly from rev hang. I drove other new cars recently when selecting my new cars and eliminated them from my list because of the severity of this unwanted "feature". My experience led me to devising my own fix.

My comments about the rev hang on Internet forums are not intended to convince car owners that they have a problem with their cars when often many owners never experience them. Rather, my comments and explanations are directed at people who noticed something strange about their revs not dropping fast enough when upshifting at higher engine speeds and wondered what was causing it. My account is meant to assure them that what they experienced is nothing new or unique, their cars are not faulty or their personal driving style is not to blame. Simply, there are technical reasons explaining why some cars behave the way they do.

gazz_bee said:

When changing gear in these circumstances, the "off-throttle" engine revs are still relatively high as you feed the clutch back in resulting in a jerky gear change. It's a bit uncomfortable for passengers and makes the driver seem uncoordinated. More concerning it's probably shortening the clutch life.

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Thank you.
Good post, and you've answered my question.

Regards,
Mick.

gazz_bee said:

I don't know if the hanging revs is a general characteristic of the 3 pot Aygo engine or if there is some software device behind the scenes so can't endorse Aquasurf's posts about this being built in to modern cars.

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Not noticed this on my swift either, even when shifting up north of 7000rpm. That said, that's obviously slightly more tuned towards spirited driving.

I wonder if this effect is at least partially to due with the weight of the flywheel- I wouldn't be surprised if the Aygo has a relatively heavy flywheel to smooth out the 3 pot engine.
jrkitching - is this sailing a bit close to the forum's trading rules, given aquasurf's posting history?

zanes said:

@jrkitching - is this sailing a bit close to the forum's trading rules, given aquasurf's posting history?

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There's sometimes a fine line between discussing an issue and promoting a product.

Aquasurf - so long as your primary purpose in posting is to contribute to the discussion about what's happening and why, I'm fine with it. If you cross over into trying to sell something, then I'm not and the usual forum policy regarding advertising will be applied.

In any case, AIUI Aquasurf's product wouldn't work on a turbocharged car so there's nothing to be sold here.

Folks also need to remember that for modern cars without a butterfly throttle valve, pumping losses (and hence engine braking) on the overrun are much reduced (which can benefit economy), and this will affect what some here have been referring to as the 'driveability' of the car.

jrkitching said:

... as long as your primary purpose in posting is to contribute to the discussion about what's happening and why, I'm fine with it.....

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Thank you, moderator, for understanding my motivation. I have no product to sell.

I get asked occasionally to drive other peoples cars, and have noticed on the new generation of petrol's (fly by wire and clutch recondition) If I floor the throttle in first gear occasionally taking the rpm up-to near the red line the revs have been held but then die as I dip the clutch again, it always seemed to be when the engine has been allowed to idle, and then going for it. As they have always performed ok when normally driven I haven't bothered about it and put it down to something sticking after being driven slow by people.

Quote from above;
"Well, what you described meets my definition of the rev hang as "an undesirable characteristic of modern cars. When throttle is closed quickly, engine speed does not drop instantly but decays slowly due to artificial delay programmed in the engine control module (ECM) by car manufacturers."

I think this may well be what I'm noticing, my Mazda too has fly-by-wire throttle but as its 2L the braking effect will be much greater and more "effective" sooner?

What definition of "hanging revs" do we use here? In my 500S there is a clear difference between what I see on the TFT display and what I hear.

My 05 Jeep has massive revs hang, my 14 Renault has it to a lesser degree, and I'm not even sure about UFI as I haven't driven it in a while you get used to these things as normal after a while, but I'm interested in the module to make it right.

What are the required connections?

UFI said:

....What are the required connections?

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In my 2012 Honda I connected the module like this: http://www.revhang.altervista.org/Diag/qrevs wiring diag.jpg.

I tested the module in 3 different car models after adjusting its software to suit each of them. This was a big deal as I could only test it in cars that I owned and had interest in, so to speak.

I built it to see if the rev hang could be removed without changes to the ECM programming and it worked. I believe my tests proved conclusively what was the cause of rev hang.