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Mark Donovan
Goo Roo
Auckland
V8 Limited, LS400

Posts: 1003
Reg: 07-2005

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Friday, December 18, 2015 - 10:40 am, by:  Mark Donovan (Mark_donovan) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Didn't know if this should be in V8 or transmission forum.

My V8 idles fine. However, if I'm driving along under throttle at about 60km/h+ and take my foot off, I can hear the engine slightly revving up and down until I next apply throttle. Is this likely ECU or IACV related, bearing in mind my ECU has been re-capped and my IACV cleaned and overhauled a few years ago?

My first line of linking was that it was maybe gearbox related, the ECU trying to figure out if to change up or down a gear.

Any thoughts?
Ekrem Vrbovac
Tinkerer
WA
V8

Posts: 30
Reg: 12-2014

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Friday, December 18, 2015 - 04:32 pm, by:  Ekrem Vrbovac (Ekremvrbovac) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I get that sometimes on my uzz31. Goes away when the car warms up.

Rarely occurs.

If you turn O/D off does it still happen? When O/D is on on mine when it hits the 4th gear, when i hit about 60 the revs again drop like its in cruise mode im guessing it's having issue dropping the revs.
Mike Beck
Goo Roo
New Zealand
UZZ32 No.32 & JZZ31 3.0GT

Posts: 6021
Reg: 11-2005

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Friday, December 18, 2015 - 08:43 pm, by:  Mike Beck (Gold_40gt) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Interesting one.

Might pay to check for any vacuum leaks.
Raoul Duke
Tinkerer
Victoria
Soarer UZZ31 V8

Posts: 41
Reg: 09-2016

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Sunday, November 13, 2016 - 09:53 am, by:  Raoul Duke (Hunter) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I'm a year late but this has happened before when solenoids in the gearbox short out too.
ECU thinks it's in 2nd, but solenoid shorts out, so maps fuel and air as 2nd gear, but it's really in 3rd gear.
It surges in 1st, 2nd, but not 3rd/OD. If anyone else sees this, check your solenoids out with the dash diagnostics.
Other causes are iacv, dirty fluid, bad plugs, bad wires, bad ecu, bad air filter, suspension leak, power steering valve leak and Engine mounts.

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