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Rb26 Droppin Rpm On Idle

4drlvr

By 4drlvr,
in General Maintenance

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4drlvr Proficient

4drlvr

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Hi Guys,

For a while now my rb26 has been having an issue only when at normal operating temp (its fine when the engines cold). Say for example if i just standing at a set of traffic lights and i rev the car, the car revs and instead of going back to idle rpm which i think is about 1100 rpm it drops way below almost turning off and then comes back to normal idle rpm. I noticed the other day if i drive the car a bit hard and then come to a sudden stop it turns off????

Ive changed bov's, checked intercooler piping, checked for vacuum hose leak, checked fuel filter, checked and made sure the afm plugs are in correctly, checked all the fuses in all the fuse boxes. Not sure what else to check, have checked the search but not much relating to this particular problem.

The engines been rebuilt only about 6000 kms and the cams havent been dialled in as yet, not sure if that makes any difference but i thought id ask.

Any help will be good

Thanks

Rj

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RB30-POWER Mentor

RB30-POWER

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clean the aac valve and idle assembly and adjust base idle rpm as per workshop manual.

if base idle is to low then the car drop rpm because the idle valve will target around 50% duty cycle by default when throttle is closed, once rpm drops below idle target rpm it will have to increase the duty cycle to bring idle back up, which gives you that result.

if the base idle is set correctly then what you get is when you pull up the idle valve is at 50% duty cycle and because you have set the idle screw to the correct idle rpm, the car will not drop past this point, in fact it will either increase or decrease rpm a bit, but it will be in the control range its intended to work, not making a big adjustment which takes some time. (in reality on a few hundredths of a second, but still time for it to drop and notice it on guage)

NOTE: if you have atmo bov will also cause this problem in alot of cases.

(to set idle on rb26, you either have to disconnect aac valve connector or disconnect throttle position sensor, search should say which method for rb26, if you get stuck wil find out for sure)

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RB30-POWER Mentor

RB30-POWER

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yeah ok, just looked for you.

warm engine to full operating temp

disconnect the aac valve connector

adjust idle screw to 900rpm (factory spec, higher if big cams in engine)

turn off vehicle

reconnect aac valve

make sure base ignition timing is good too at the same time.

Edited by RB30-POWER
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4drlvr Proficient

4drlvr

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Thanks guys for the reply, ive cleaned the aac valve on an rb25 before but i just looked at the engine bay and cant find it on the rb26???

Does anyone have a pic of where it sits on the rb26??

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Hydroxinol Enthusiast

Hydroxinol

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I had the same issue. Check your O2 Sensor. Warm the car to the point where the idle starts to suffer and disconnect the O2 Sensor. Wait a while and see if the idle smoothes out. If it does, it's a problematic O2 Sensor.

You can also test the O2 Sensor with a multimeter to check that it constantly varies between 0-1V when at operating temp.

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Dohmar Grand Master

Dohmar

Posted
Posted
Hi Guys,

For a while now my rb26 has been having an issue only when at normal operating temp (its fine when the engines cold). Say for example if i just standing at a set of traffic lights and i rev the car, the car revs and instead of going back to idle rpm which i think is about 1100 rpm it drops way below almost turning off and then comes back to normal idle rpm. I noticed the other day if i drive the car a bit hard and then come to a sudden stop it turns off????

Any help will be good

Thanks

Rj

Same sort of thing happened to me when one of my AFM's were going out, would be driving along and then the car would shudder, lose power for a second or so, then go back to working... it slowly got worse and once while Idling it just cut out completely. While it might not be the AFM, thats one thing I could think of to check, perhaps get a couple from a friend and drive it for a day and see how it goes... I ended up buying two off the forum and the first one I swapped worked fine, havent had any problems since

-D

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GeeTR Grand Master

GeeTR

Posted
Posted (edited)
Thanks guys for the reply, ive cleaned the aac valve on an rb25 before but i just looked at the engine bay and cant find it on the rb26???

Does anyone have a pic of where it sits on the rb26??

Go deep, its under the plenum. If i rem, ill chuck up a pic from my pull down collection.

EDIT: Cheated and found a suitable picture from Derens Outa Control BNR32 Restoration thread (sorry for large picture)

Below, it goes where theres an open flange, at the front of the collector thing'a ma'bang jizzle, just above the yellow plug.

I think :cool:

CLICK FOR PICTURE

Edited by GeeTR
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HELLRAISER Explorer

HELLRAISER

Posted
Posted
Hi Guys,

For a while now my rb26 has been having an issue only when at normal operating temp (its fine when the engines cold). Say for example if i just standing at a set of traffic lights and i rev the car, the car revs and instead of going back to idle rpm which i think is about 1100 rpm it drops way below almost turning off and then comes back to normal idle rpm. I noticed the other day if i drive the car a bit hard and then come to a sudden stop it turns off????

Ive changed bov's, checked intercooler piping, checked for vacuum hose leak, checked fuel filter, checked and made sure the afm plugs are in correctly, checked all the fuses in all the fuse boxes. Not sure what else to check, have checked the search but not much relating to this particular problem.

The engines been rebuilt only about 6000 kms and the cams havent been dialled in as yet, not sure if that makes any difference but i thought id ask.

Any help will be good

Thanks

Rj

Hey Mate

Is it something like this that happens to you

http://www.youtube.com/watch?v=rOpZKjtmlJM

pls let me know whats the cause if you figure it out ...

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4drlvr Proficient

4drlvr

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Posted (edited)

Hi People

Got a chance today to try out what you guys told me but instead of taking the aac out to clean it, what i did was when the car is at running temp i took the connection out from the AAC and nothing happened. My question is was the RPM meant to drop.

Also when i unplug the TPC connector from the throttle rale nothing happens either, i would have thought that the RPM might have dropped??

Can some please shed some light on this and since there is no change when i unplug the connection to the AAC is it worth takin it out and giving it a clean????

By the way "HELLRAISER" thats exactly wats happening, exept wen i rev the engine it the pm wont drop all the way to "0" it will hunt between 400 to about 800 RPM i rekon but if i drive it hard and then come to a sudden stop the car just turns off???

HELP!!!!

Rj

Edited by 4drlvr
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RB30-POWER Mentor

RB30-POWER

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Posted

revs should rise when the aac connector is plugged back in after adjusting the base idle as per the procedure i posted above, by around 50rpm or so (will hear it change when plug it back in)

if no change is present either the aac valve is faulty or the driver circuit in the ecu.

easy way to test the aac valve is to unplug it and put +12 across the terminals and listen if it clicks fully open (will hear it click if its working)

to test the ecu driver circuit get a injector noid light (from bursons/repco $15) and plug it into the aac harness plug and see if it on or flashing.

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