N12Turbo.com lanyards are now available! Click here to visit the shop

Retain Cold Idle Post Log-Removal.

All complete technical articles moved here after review
User avatar
Posts: 79
Joined: Wed Jun 05, 2013 12:27 am
Location: Adelaide, Australia

Retain Cold Idle Post Log-Removal.

Post by KiloooNL »

Hi everyone, here is a method of retaining cold idle after removing the log that myself, and others have used that is neat & tidy.

To start with, the log contains 2 air regulators. One is the ICV (Idle Control Valve) with the 3 adjustment screws and the other being the small black Cold Air Regulator.

Essentially in this guide, we will be removing the log and replacing the ICV & Cold Air Regulator with a cold air regulator from an RB30 engine. This can also be found on most early EFI engines at wreckers.
This unit can be had for a couple bucks more or less.
For this cold air regulator, we use the 12v connector from the stock cold air regulator.
The connectors for the ICV are not required here.

Things you will need:
- RB30 Cold Air Regulator
- Length of hose to suit the cold air regulator
- Drill & drill bits
- Spare bolts
- Pipe with bung to suit, or DIY pipe with bung tube.
- Length of 5mm mild steel. A) For blocking off intake manifold coolant channels. B) for throttle cable bracket
- An IQ above 10.

Step one:

To start with, once you have removed the log you will notice the 2 coolant channels that the log 'blocked' off below, circled in red.
You will need to make up some small plates with a hole drilled in each to bolt to the thread.
Although not pictured, I used 5mm mild steel.
If you happen to break the gaskets, simply make some new ones with gasket paper.

Step two:

Once you have sorted that, grab your cold air regulator and drill out the holes.
We will be placing the regulator on the back of the head, but the bolt holes on the regulator need to be enlarged so the bolts line up with the head threads.

Picture 1 shows the air regulator after the bolt holes have been drilled out larger.
Picture 2 & 3 show where on the back of the head we will bolt the air regulator to.

Step three:

Now that you have bolted the air regulator to the head, as seen below (picture 2), you can connect the 12v stock cold air reg connector to the unit.
Next you will need to make up a small pipe with a tube bung to attach the hose to in the intake piping.
I simply welded one up with the MIG, if you don't have an intercooler and are using the stock intake piping then you would have to attach a bung to the piping, or make up a new piece.
I used 15mm steel tube for this bung.

What exactly do I mean? Something like this:
Connect one end of the hose to the tube bung you made up, and the other end to the intake plenum where the stock ICV hose plumbs back to, as shown in the pictures below.

If you are using this guide for referencing a different way to do the AFM relocation, the PCV breather hose needs to be plumbed in PRE-turbo.
This can be achieved by using the stock elbow where the PCV hose connects on the stock system, or alternatively by making up an additional
pipe with a tube bung, similar to that which you will need to do for the cold air reg installation.
NEVER connect the PCV breather hose POST-turbo.
Step four:

Now that everything is connected & plumbed back, feel free to give the engine a start and observe the cold idle RPM.

If the RPM is too high, or too low, you are able to adjust it using this little 7mm nut as pictured below.
Simply loosen the nut and move it back and forth to find the desired RPM then tighten.
Now that the cold idle has been set, once the engine has warmed up we will have to set a warm idle. This will have to be set via the throttle screw to the right of the throttle body, as circled below.

When setting the warm idle RPM, apply load (turn on headlights, air con, heater, etc) and then set the RPM to at least, 750rpm.
Then turn off the accessories and re-check the RPM to ensure its within a desired range.

The reason for this, is because we have removed the ICV we no longer have control over the idle to a degree when load (acc) is factored in.
So by raising the RPM with the load off, we have headroom when using accessories.

After doing this, you will need to plug in a multimeter and check the TPS is set correctly and adjust accordingly, there is every possibility that this will throw off the TPS switch, so adjustments may be needed.

This guide will be updated in the future to use a valve solenoid to control load based idle RPM.
Step five:

Because we have removed the log, there is no longer a bracket for the throttle cable.
There are a few options here.
Number 1: Cut the log down where the throttle cable bracket bolts to, and bolt that section of the log back on. As shown in the first picture below.

Number 2: Make up a custom throttle cable bracket.

The pics below are some examples of other N12's with these styles of brackets.

Final thoughts:
This is just how I did my setup. I find it an alternative and much neater way to do the AFM relocation while retaining cold start with the log removed.
I welcome any feedback on this setup!
This guide was put together in about 30 mins so I may revise once I read thru again.
A big thanks to E and all the other fellas that helped out on the setup!!

I plan to add more info in the future, as noted above, using a solenoid valve as a means of ICV, which is a better way of controlling on-load idle RPM.
Enjoy the extra space with the log removed!
Here's an indication of what the bay looks like.
Note the PCV breather hose and the small tube bung I made up for it if you intend on doing that below.