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Author Topic: RB26DETT High Idle Issue  (Read 2890 times)

SlaterRacingNZ

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RB26DETT High Idle Issue
« on: May 23, 2016, 10:55:34 AM »
Hi Guys.

I've had a high idle problem with my rb26 ever since I've had it.
It was disassembled completely and put back together before we dropped it in the hole.
During the process the Throttle Bodies where cleaned, which more than l likely caused the high idle issue.
I'd recently removed my plenum to repaint it, and decided to clean the throttle bodies again.

Much to my surprise the idle has now jumped up to 1500 rpm from 1300, so more or less it's time to get to the root cause of it now.
Normally I wouldn't ask on forms for any form of guidance or help, but this time it's more than likely something someone's already dealt with.

I've trawled through a fair few forum articles on this issue, and have found the common cause to be a vac leak.
So am thinking of doing the following, before eventually pulling the plenum off again and attempting to reseal the throttle blades.

Attempt to Remedy Issue:

-Double check for any vac leaks .
-Remove AAC and thoroughly clean it with Carb Cleaner.
-Assemble AAC and leave unplugged .
-Unscrew IAC adjustment till flush. (Currently screwed in all the way)
-Fire the car and attempt to lower idle via screw, if successful shutdown the car and refire with the AAC plugged in.
-If no joy but idle has dropped substantially, attempt to adjust ecu idle screw.
-If no joy put ecu adjustment back to factory, then zero out Throttle Body stops.
-Zero out the Throttle Drum stop, insert 1mm feeler gauge between throttle drum to throttle drum stop.
-Adjust linkages to point of resistance and back off 1/3th a turn. (Set tps to .5v after adjustments are complete)
-Fire the car and see if anything's changed.

So if all that fails then I'd like to take the car down the road, and pressurize the intake to check for leaks.
Should there be none then the plenum will come back off, and I will attempt to reseal the throttle plates.
I've a reasonably good system in my head for how to leak test the intake system, using tdc, an air compressor, a manual boost tap, and a boost gauge.

Anyway point of this whole post was to ask if anyone has resealed their rb26 throttle bodies, and what sealant you used and where you got it from in nz?
Because I'm 84.3% sure it's the cleaned throttle bodies causing my high idle issue.

gtsr

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Re: RB26DETT High Idle Issue
« Reply #1 on: May 23, 2016, 07:38:43 PM »
Hi Guys.

I've had a high idle problem with my rb26 ever since I've had it.
It was disassembled completely and put back together before we dropped it in the hole.
During the process the Throttle Bodies where cleaned, which more than l likely caused the high idle issue.
I'd recently removed my plenum to repaint it, and decided to clean the throttle bodies again.

Much to my surprise the idle has now jumped up to 1500 rpm from 1300, so more or less it's time to get to the root cause of it now.
Normally I wouldn't ask on forms for any form of guidance or help, but this time it's more than likely something someone's already dealt with.

I've trawled through a fair few forum articles on this issue, and have found the common cause to be a vac leak.
So am thinking of doing the following, before eventually pulling the plenum off again and attempting to reseal the throttle blades.

Attempt to Remedy Issue:

-Double check for any vac leaks .
-Remove AAC and thoroughly clean it with Carb Cleaner.
-Assemble AAC and leave unplugged .
-Unscrew IAC adjustment till flush. (Currently screwed in all the way)
-Fire the car and attempt to lower idle via screw, if successful shutdown the car and refire with the AAC plugged in.
-If no joy but idle has dropped substantially, attempt to adjust ecu idle screw.
-If no joy put ecu adjustment back to factory, then zero out Throttle Body stops.
-Zero out the Throttle Drum stop, insert 1mm feeler gauge between throttle drum to throttle drum stop.
-Adjust linkages to point of resistance and back off 1/3th a turn. (Set tps to .5v after adjustments are complete)
-Fire the car and see if anything's changed.

So if all that fails then I'd like to take the car down the road, and pressurize the intake to check for leaks.
Should there be none then the plenum will come back off, and I will attempt to reseal the throttle plates.
I've a reasonably good system in my head for how to leak test the intake system, using tdc, an air compressor, a manual boost tap, and a boost gauge.

Anyway point of this whole post was to ask if anyone has resealed their rb26 throttle bodies, and what sealant you used and where you got it from in nz?
Because I'm 84.3% sure it's the cleaned throttle bodies causing my high idle issue.

I believe a common problem, most likely the seals for the throttle plate shafts on the throttlebodies have been damaged when cleaning with carb cleaner (eats seals) and are leaking (they warn about not cleaning near the seals). Or like you said, throttleplates are not sealing to body of throttlebody as removed the sealing compound.

I believe they use a Permatex sealing compound. Would have to contact Permatex to ask which sealant it is -

https://www.permatex.com/

It's a non hardening sealant.

Also some throttlebodies have a air bypass screw on them.

If stock ECU, need to put ECU into idle adjustment mode via Consult, unplug AACV so it doesn't play with idle rpm and adjust to idle rpm in manual (950rpm? for RB26). It displays rpm on Consult, so easy to adjust. If can't, ask a Nissan tech at Nissan dealership to do it for you. Or find Conzult, Consult cable, as should be able to do the same adjustment.

Adjusting via screw on side of ECU is tricky, as it can adjust idle rpm 250rpm higher at a time when adjust to the right back to run mode. Easier / better via Consult.

Also I would check battery voltage, as ECU might be compensating for low voltage via battery compensation (rasing idle rpm).

Also check o2 sensors (lazy fluctuations) if connected.

SlaterRacingNZ

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Re: RB26DETT High Idle Issue
« Reply #2 on: May 24, 2016, 06:57:05 AM »
I believe a common problem, most likely the seals for the throttle plate shafts on the throttlebodies have been damaged when cleaning with carb cleaner (eats seals) and are leaking (they warn about not cleaning near the seals). Or like you said, throttleplates are not sealing to body of throttlebody as removed the sealing compound.

I believe they use a Permatex sealing compound. Would have to contact Permatex to ask which sealant it is -

https://www.permatex.com/

It's a non hardening sealant.

Also some throttlebodies have a air bypass screw on them.

If stock ECU, need to put ECU into idle adjustment mode via Consult, unplug AACV so it doesn't play with idle rpm and adjust to idle rpm in manual (950rpm? for RB26). It displays rpm on Consult, so easy to adjust. If can't, ask a Nissan tech at Nissan dealership to do it for you. Or find Conzult, Consult cable, as should be able to do the same adjustment.

Adjusting via screw on side of ECU is tricky, as it can adjust idle rpm 250rpm higher at a time when adjust to the right back to run mode. Easier / better via Consult.

Also I would check battery voltage, as ECU might be compensating for low voltage via battery compensation (rasing idle rpm).

Also check o2 sensors (lazy fluctuations) if connected.

Haven't personally been this active in a while, and was very surprised to get an indepth response like this.
As always gtsr you never disappoint :)

I had a look at permatex form a gasket no1 sealant just before making this article, it looked like a good last resort over the gm dag213.
https://www.permatex.com/products/gasketing/permatex-form-a-gasket-no-1-sealant/

There has been some compelling results and divided opinions regarding rtv on the throttle plates edge.
If itbs have some form of sealant on the throttle plates from factory, or weather it's just carb\oil build up over time that's scraped off.
I'm kinda on the fence regarding the sealant, as over time it could wear off and make it's way through the combustion cycle.
Others suggest the throttle body inside diameter must align with the outside, which would indicate no sealants required.

Here's some useful info I found on resealing itbs:
http://forum.miata.net/vb/showthread.php?t=521573

Anyway, an update on the issue:

I've had a parasitic draw on my battery for a solid couple of years now, so the battery would always go flat within a week or so.
During all the changes I've managed to fix that issue (not pertaining to the car stereo either), and ended up doing a few idle voltage tests as well.
So a brandnew battery was installed, and voltage from both the battery and engine bay fuse box tested. (12.5v resting, 14.4v running)

It's about time I got an odbc scanner tool for my phone, would certainly save me plenty of future headaches.
I'd really like to test the o2s, but am pretty comfortable they're in reasonably good condition. 
Afms were crc maf cleaned before the Edlebrock filters were installed, and all turbo\instake side lines were inspected for leaks and proper sealing.

I cleaned the itbs with a tooth brush dipped in fuel, decided against using carb cleaner on something so delicate.

So yesterday I didn't even start with the aac, as it just felt like I should attack the throttle plate stops first.
Removed the fuel rail even though I probably didn't need to, and backed off the throttle plate stops.
Disconnected the linkages from the throttle drum assembly, and backed the plate stops right off till I could feel the plates bind on the bores.

I slowly adjusted each one till they didn't bind and then locked all the throttle plate stops. 
Then slotted a 1mm feeler gauge between the throttle plate stop and throttle spring stop, and pulled it out to feel the resistance was the same on all.
No pictures unfortunately but you can see the screw I'm on about in the right corner of these throttle bodies.



Then did the final adjustments on all the linkages, so they all smoothly slotted onto their locators.
At this point I run out of time and had to go out, so quickly put the fuel setup all back together and fired the car.
While I could feel the throttle plate bind on throttle bodies 1 and 2, I couldn't feel the 3rd nearly as good.
So I'm going to readjust the linkages tonight, given I'll have a lot more time to do it.

After doing this I managed to lower the idle from 1500 down to 1100, with the aac screw adjusted in all the way.
Even reset the aac with it unplugged and backed the screw right off before firing the car, could only get it to go down to 1100.
It jumped up to 1500 when the aac was plugged in, but quickly ramped down to a stable 1100 warm up idle.

Before I even touch the linkages tonight, I'll carb clean the shit out of the aac and make a new gasket for it.
Reassemble it and warm the car right up, and see if the revs drop below 1000. (Ideally looking for 950rpm warm).
If this doesn't work I'll try adjust the throttle plate stops once more, as my aim is not to touch the ecu's idle adjustment screw.

Here's hoping it's as simple as carb cleaning the aac, all though it feels like if I clean the aac that the idle may increase further.
« Last Edit: May 24, 2016, 07:16:16 AM by SlaterRacingNZ »

SlaterRacingNZ

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Re: RB26DETT High Idle Issue
« Reply #3 on: May 25, 2016, 10:32:55 AM »
Update: Adjusted throttle plate stops again, and also the linkages to suite the supplementary changes.
-Idle now 1050 rpm with the AAC screw adjusted all the way in.
-Was stable during warm up, but once at operating temp it crept up to 1300.

The idle remained at 1050 (Cold) before the aac was cleaned, but I never fully warmed it up to operating temp.
My understanding is the IAC is responsible for cold and warm start idle control, is my issue perhaps with iac and not the aac.
I attempted to adjust the ecus idle screw but it was already set on the lowest setting, and also complete the aac reset procedure.

I'm thinking maybe I'm being to soft in the Throttle Plate stop Adjustments, and maybe there's actually such thing as a "Special Throttle Plate sealant".

Maybe I should also carb clean the iac......

For the 3rd time this week I'll adjust the throttle plate stops again, this time the plates will pretty much be on the point of bind.

gtsr

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Re: RB26DETT High Idle Issue
« Reply #4 on: May 26, 2016, 04:52:05 PM »
Update: Adjusted throttle plate stops again, and also the linkages to suite the supplementary changes.
-Idle now 1050 rpm with the AAC screw adjusted all the way in.
-Was stable during warm up, but once at operating temp it crept up to 1300.

The idle remained at 1050 (Cold) before the aac was cleaned, but I never fully warmed it up to operating temp.
My understanding is the IAC is responsible for cold and warm start idle control, is my issue perhaps with iac and not the aac.
I attempted to adjust the ecus idle screw but it was already set on the lowest setting, and also complete the aac reset procedure.

I'm thinking maybe I'm being to soft in the Throttle Plate stop Adjustments, and maybe there's actually such thing as a "Special Throttle Plate sealant".

Maybe I should also carb clean the iac......

For the 3rd time this week I'll adjust the throttle plate stops again, this time the plates will pretty much be on the point of bind.

You're welcome. :)

I haven't been here in a while too.

I have had high idle issue when AACV was adjusted incorrectly, TPS adjusted incorrectly (not touching idle contact), o2 sensor was faulty (would get idle rpm going up and down. When engine goes rich the rev needle goes down and rev needle rises when engine goes lean), low battery voltage, AFM has failed (idles around 1500rpm when cold, warm and unplugging both AFM's should eliminate this, and is a stock ECU only feature where you can unplug AFM's before starting engine to check for faulty AFM's. But need to clear error code on ECU which is as easy as removing negative battery cable and pressing brake pedal a few times, then refitting negative battery cable), intake air leak just before throttlebody.

The IACV can stick open causing high idle issue due to oil deposits from blown turbo oilseal or excessive blowby. A NIssan tech told me there is an adjustment screw on the IACV (on some Nissan IACV there is, I think SR engines or similar 4 cyl engines). In rare cases the IACV has failed and needs to be replaced. Blocking IACV off, air feed to IACV off when engine is warm, then starting engine to check should eliminate the IACV as a cause of high idle.

But you can test IACV on a hot plate with voltage to IACV (how manual mentions to test it). It works via heat from engine when warming up (why it is placed close to engine), voltage. The IACV should close fully in 9-10 minutes or so (mentioned in manual) and meant to time the time it takes to fully close. Too long or not at all, you need to replace the IACV.

If ECU is causing high idle, unplugging AACV plug should stop ecu playing with rpm and should drop back to what IACV idle rpm adjustment screw is set at.

GQDZLA

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Re: RB26DETT High Idle Issue
« Reply #5 on: September 05, 2016, 11:54:04 AM »
hey guys you sound on the money, how about an RB26 that runs fine unless you stop or slow down from motorway speed to 50kph and the motor then 5 mins later splutters and pops, looses all power and couldnt pull it self out of the gutter??  the idle can go all over the show and motor often revs up and down by itself and 5 min later may run fine again? got new plugs, coils, coil loom and swapped out the ignightor pack and water temp sensors, AFM have been cleaned but not tested for electrical issues, whats the guess on this chaps??? stock motor stock ecu
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