_Matt

Nissan v8 idles high until turned off and on

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The VH41de in my pickup has had an issue for a little while, where it will idle somewhere around 1000-1200rpm, it’s like it stays on cold start or the throttle is sticky. Seems to do it more often if doing lots of shorter trips. It doesn’t drop down until you turn it off and back on, then sits somewhere around 5-600 rpm. I don’t think it’s transmission related as it’s on it’s third trans and has done it for all of them. That’s another issue that need sorting. 
I have checked most of the sensors and the voltage readings seem about right to the manual. Anything else I could check?

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pics of throttle body?

from memory the 41 has a wax thermostat expandy thing on the bottom of the throttle body that ups the idle for cold start and the hot water pipes warm it up and make it back off.

could be sticky.

 

or as above, pull the aac valve off and give it a lube up

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Sweet thanks guys! Will pull it apart sometime and have a look.

Not great pics, but all I have atm. Throttle body has the extra throttle sensor and solenoid? for traction control I think.

43776058370_ff320d141e_o.jpg

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12 minutes ago, _Matt said:

 

43776058370_ff320d141e_o.jpg

thats the idle air (AAC valve) behind the throttle cable bracket. give that a strip and clean first

the 2nd throttle cable attachment is for the cruise control actuator cable, and the cam bit behind that is to make the throttle open slowly at first to make it easier to control at low rpm

 

 

 

 

that black cylinder is the traction control motor. it drives a 2nd butterfly in front of the main throttle and shuts when it detects you having fun

Quote

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Hey @fletch, I have cleaned out the AAC valve and it made no difference.

Then I got a whole new throttle body, which included a different AAC valve and bolted that all up. Again made no difference.

I did notice the coolant isn’t hooked up to flow through the throttle body. I don’t think that should be causing this issues though. I did also back the adjusting screw that the AAC valve pushes and moves the throttle linkage up all the way out, so it shouldn’t idle up from that anymore. That also made no difference. 
Another thing to add is when you give it a decent rev at idle it will start idling even higher, not sure if it does it all the time or just when it’s already idling high though. 

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Throttle cable binding somewhere/sticking? Could disconnect and see it it helps

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Vacuum brake booster leak? Cant remember if you were running a booster. Try disconnect that?

 

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The fact that it comes right once you power cycle the ECU suggests it could be ECU related, given that nothing would have changed on the mechanical front during the power cycle.

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Are any of the vacuum lines hooked up differently to the stock setup?

In my old MR2 it had a smallport 16v motor setup which came from a FWD car with power steering, It always had a high idle when I got it.

After reviewing another 16v smallport in a stock car at pickapart I carefully made note of what each of the lines connected to the TB did and worked out the powersteer idle up lines were looped (no PS in aw11 mr2). I blocked them off instead of looping and that sorted my problem.

You might have a similar problem with lines being capped/looped?

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Thanks guys, will have a check over all that. I’m pretty sure the butterfly/throttle linkage is closing properly, as I gave it a push down and the idle barely drops at all. 
It is running a vacuum brake booster and the other couples of vacuum lines are blocked off. 
I have been thinking it has been electrical for awhile, because of the power off and back on, then it comes right, but trying to find another ecu has proven a bit difficult. 

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Pull open the existing CPU and check condition of the electrolytic capacitors - if you see any bulging or signs of leaking then they could be your problem.

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4 hours ago, fuel said:

Pull open the existing CPU and check condition of the electrolytic capacitors - if you see any bulging or signs of leaking then they could be your problem.

Ahhhh will have a look, thanks. Knew this was a common issue with 4age 20v Ecu’s. Didn’t think to check on this

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3 hours ago, thegreatestben said:

Ling post but I would chuck some $$ in a hat to see this thing get an aftermarket ECU.

Also keen on that, but that’s a lot of $$$. Have a bellhousing and clutch setup to suit a w series manual box, which will make it way more fun to drive!

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Pulled out the ecu and opened it up. Everything looked good. 
Only problem I could see, there was a dent on the under side located where the JECS logo is in the lower left. It was pushed in enough for the cover to be indented from the board and those pins coming off the plug. 
Maybe that has caused something to short out? Wasn’t anything noticeable.

02kWae4r.jpg

 

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31 minutes ago, Grotty said:

is the idle valve a stepper motor on that? 

The AAC valve? If so, I’m not too sure, quite possibly?

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