Jump to content
SAU Community

RB25 DET idle speed control on heavily modded engine

Recommended Posts

I am heavily modding a Nissan Skyline R33 GTS-t RB25 DET engine. Big

external wastegate turbo, 280 duration cams, steel internals, Motec ECU, blah blah.

My question is idle speed control related. Why did Nissan have 3

separate means of idle speed control? It has a bi-metallic strip cold

start idle up device under the plenum, a solenoid for A/C on and PAS

load idle up, and a stepper motor device for normal idle speed control

(and a throttle butterfly and accelerator pedal of course... :-)) My

goal is a track day car, perfect idle control isn't too high on the

agenda, A/C is ditched, and with the cams a fairly high idle is needed

anyway (1200 RPM or so). Emissions aren't too much of a worry either. As

such should i just run a conventional stepper motor idle control and

blank off the other 2?

I am confused as to why Nissan didn't just use the stepper motor to

control the idle though, it seems unnecessarily complex.


Link to comment
Share on other sites

The Nissan AAC valve is not a stepper motor. It is a solenoid valve which is fed a PWM signal (constant frequency - duty cycle varies from 0 - 100%) from the ECU. My guess is this valve alone dosn't flow enough air to keep the idle high enough when under extreme load. i.e engine still cold, a/c on, power steering pump under heavy load. If they made it flow higher, it probably wouldn't control accurately.

I'm running a Haltech E11 ECU on my RB30DET. I still have the cold air bypass valve hoses connected (but no power to the valve). The a/c idle-up solenoid is disconnected and the haltech drives the AAC valve. Cold idle is set to 1200rpm and warm idle is set to 850rpm and it controls well, although the idle can drop to 700 if the a/c is on. Hope that helps.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

  • Latest Posts

    • Hey all, my V35's front balljoints and lower control arm bushes are shot, so will have to buy some new ones. Just want to check if these are the correct ones and if y'all have any places within AU that supply these parts, or would I be better off shipping some in from the US (z1, concept z, etc)? I'm currently in ACT.  I'm looking for sparkplugs as well but can't seem to find them locally. I found this site that sells Mevotech ball joints: https://www.kudosmotorsports.com/catalog/front-ball-joint-lower-outer-nissan-z33v35am35-p-1990.html Lower control arm: https://justjap.com/products/sterling-front-lower-control-arm-r-h-straight-fits-nissan-m35-stagea-v35-skyline-z33-350z?variant=44217571377351&currency=AUD&utm_source=google&utm_medium=organic&utm_campaign=Advanced feed&utm_content=Sterling Front Lower Control Arm R%2FH (Straight) Fits Nissan M35 Stagea%2C V35 Skyline %26 Z33 350Z&utm_campaign=gs-2022-07-20&utm_source=google&utm_medium=smart_campaign&gad_source=1&gclid=CjwKCAjwps-zBhAiEiwALwsVYYAaGCq4d8TaCWYiuo62l_F9zi69FBW9ErruC5gpxu_euNqnxjPa_BoC6FcQAvD_BwE
    • Hey just wanting to know if a R34 gtr wheel hub will bolt onto a R34gt rear knuckle?  I am doing a 350z lsd conversion and I came across an issue with the rear axles fitting into the wheel hub as the spline count is different. I think the r33/4 (GTR)wheel hubs are 32 spline while the standard 3x2 rear axles are about 28,  the 350z rear axles I’m using are also 32 spline so I don’t see why it won’t fit apart from where the hubs bolt onto the knuckle  I am not 100% sure about any of this and would like some info before I go mix n match and help would be appreciated.🙏  
    • There is none when used in the radius rods. I am a strong advocate of sphericals in that location.
    • Oh damn, thats seriously cool. I have the Thrustmaster T248 which is the entry level one. Its really good but I have no basis for comparison as I've never used a better one. I'd like to change the pedals for the pressure ones (cant remember the name) and get a proper frame and seat because I just have a stand for the pedals and wheel now and I need to brace them against things so they dont move when I'm trying to pull up after a long straight! 🤣 EDIT: These ones; https://www.thrustmaster.com/products/t-lcm-pedals/
    • Pulled the lazy pin and ordered the 4 new calipers for just over $600
  • Create New...