4.8 how to disconnect high idle on start
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Hi Morton,
First a disclaimer that I know nothing of 4.8 patrol engines, but EFI systems use what's called an idle air control valve which is an air bypass controlled by the ECU. This valve regulates the idle speed by allowing air to bypass the butterfly. There is really nothing a layman can do, maybe the parameters for startup could be adjusted in the ecu by a mechanic with access to the nissan's brain (but as I say I don't know these engines at all). You could experiment by disconnecting the plug from the IAC while it is idling leaving the stepper motor 'parked' in that position, but it would most likely then stall on cold starts and under loads like your air conditioning etc. It may also throw a fault code which may be inconsequential or disasterous. (My one and only EFI was a Rover V8, which was a pretty dumb system)
Cheers
Dan
First a disclaimer that I know nothing of 4.8 patrol engines, but EFI systems use what's called an idle air control valve which is an air bypass controlled by the ECU. This valve regulates the idle speed by allowing air to bypass the butterfly. There is really nothing a layman can do, maybe the parameters for startup could be adjusted in the ecu by a mechanic with access to the nissan's brain (but as I say I don't know these engines at all). You could experiment by disconnecting the plug from the IAC while it is idling leaving the stepper motor 'parked' in that position, but it would most likely then stall on cold starts and under loads like your air conditioning etc. It may also throw a fault code which may be inconsequential or disasterous. (My one and only EFI was a Rover V8, which was a pretty dumb system)
Cheers
Dan
Leave it well alone it's supposed to idle high at start up for a multitude of reasons.
Cheers
Justin
Cheers
Justin
Are you sure these things don't also have an Air reg/cold start valve?
My experience is with Rb's and they all have the AAC valve to bump idle for aircon, power steer loads etc, it's the normal ecu-controlled idle valve.
But they also have an Air Regulator for cold starts. This is a separate air circuit controlled by a 12V bi-metallic strip valve on early Rb's and by coolant temp on later engines.
It's simply not needed in our climate. In every Rb I've owned, I plug all the air reg air pipework and the AAC still controls the idle perfectly, even on Winter mornings with ice on the windscreen.
My experience is with Rb's and they all have the AAC valve to bump idle for aircon, power steer loads etc, it's the normal ecu-controlled idle valve.
But they also have an Air Regulator for cold starts. This is a separate air circuit controlled by a 12V bi-metallic strip valve on early Rb's and by coolant temp on later engines.
It's simply not needed in our climate. In every Rb I've owned, I plug all the air reg air pipework and the AAC still controls the idle perfectly, even on Winter mornings with ice on the windscreen.
The idle control valve is controled by the electronic throttle motor on this engine then by the ecu unfortanulty this is the way this engine is. you could try taking the throttle body off and giving it a good clean then doing a idle air learn and throttle position reset
reving to 2000 rpm on a cold motor isnt a bad thing, its not under load. when you rebuild a motor they recomend you to rev the motor up to 2000 rpm and hold it there, this is because there is plenty of oil being circulated to all parts of the motor with ample pressure during the cam bed in. thats on a virgin motor so i would hardly be concerned about doing the same thing to a cold motor.
i would how ever be looking into why the timimg chain is rattling
my 4.8 doesnt rev to 2000 rpm on start up so like someone else said maybe try the idle relearn
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