Author Topic: Rev needle - foot off gas and still moving  (Read 2519 times)

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  • HOS BOSS
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Rev needle - foot off gas and still moving
« November 16, 2008, 11:03:56 »
When driving take foot of gas the RPM's will drop. (Normal engine function).

However, the RPM needle does not drop to idle RPM but will hovers just above 1000 rpm.

It doesn't drop to below 1000 rpm at any point whilst moving.

It only drops to below 1000 rpm when stopped.  It then idles around 8/900 rpm.

Anyone else noticed this?


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Re: Rev needle - foot off gas and still moving
« Reply #1 : November 16, 2008, 11:14:22 »
Isn't this what some call the anti-stall feature?

Mine behaves exactly the same. When stopped at lights, the revs stay at 1000rpm for about 5 seconds then drop to around 800. When in gear and moving, around 1100
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Re: Rev needle - foot off gas and still moving
« Reply #2 : November 16, 2008, 13:53:23 »
the i30 uses fly by wire throtle, just because you put your foot down or take your foot off, does not mean the throtle at the fuel delivery will imitate you. it's all computer controled. a lot of new cars and motor cycles use this type of throtle now. i like it now but when i first started useing it with my ford falcon, i did not like it, but got used to how it works and love it now, with the ford they downloaded upgrades and the ute felt like it had more power.
cheers

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Re: Rev needle - foot off gas and still moving
« Reply #3 : November 16, 2008, 15:52:17 »
Let me guess, you only notice this when it is very cold outside?  8-)

The hotter it is, the quicker the RPM's will come back to normal (700-800rpm) for idle.

Yesterday, 36 degrees C, idle drops back very quickly once everything is warm.

During winter here (-8 degrees C) idle will hang around 1,000rpm for a while (Up to 2 minutes) before slowly dropping down.

I believe it's to make sure the catalytic converter (Opps, I mean Diesel Oxidation Catalyst) remains hot and effective.

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Re: Rev needle - foot off gas and still moving
« Reply #4 : November 18, 2008, 15:12:54 »
The petrol is much the same guys, I can get mine to drive off out of my drive without touching the loud pedal first thing on a frosty morning.
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  • HOS BOSS
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Re: Rev needle - foot off gas and still moving
« Reply #5 : November 18, 2008, 15:26:10 »
Quote from: "Thumper"
Let me guess, you only notice this when it is very cold outside?

No. It happen all the time. Hot/cold/rain/snow.
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Re: Rev needle - foot off gas and still moving
« Reply #6 : November 18, 2008, 15:27:57 »
Quote from: "eye30"
Quote from: "Thumper"
Let me guess, you only notice this when it is very cold outside?

No. It happen all the time. Hot/cold/rain/snow.
Hey eye30.. where the hell do you get the "Hot" bit from  :?
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Re: Rev needle - foot off gas and still moving
« Reply #7 : November 18, 2008, 15:32:19 »
Mebbe it's his wife :?:  :oops:
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Re: Rev needle - foot off gas and still moving
« Reply #8 : November 18, 2008, 15:34:49 »
Quote from: "Shambles"
Quote from: "eye30"
Quote from: "Thumper"
Let me guess, you only notice this when it is very cold outside?

No. It happen all the time. Hot/cold/rain/snow.
Hey eye30.. where the hell do you get the "Hot" bit from  :lol:

Oh sorry missed windy off the list. :oops:
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Re: Rev needle - foot off gas and still moving
« Reply #9 : November 19, 2008, 04:16:41 »
I reckon its to do with vacuum boosted braking system.  Diesels do not have manifold vacuum, so the vacuum for the brakes is generally supplied by a pump fun off the back of the alternator.  While you are moving, the computer has the engine revs a little higher to keep a good supply of vacuum to the brake booster.  Not sure on this but I think it may be the case.

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Re: Rev needle - foot off gas and still moving
« Reply #10 : November 19, 2008, 05:34:26 »
It's actually a pump that runs off the timing chain/cam, on the battery side of the head. (Tube runs to the turbo and to the booster)

When you take the big black cover off the top of the engine you'll see what I am talking about.  8-)

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Re: Rev needle - foot off gas and still moving
« Reply #11 : November 19, 2008, 05:52:05 »
Thanks Thumper.  I'm reluctant to take the cover off, I might get tempted to tinker.  Still the same principle at play with the engine revs tho I think.  Could have other reasons too but this would be a major factor in the ECU logic.