Toyota Corolla AE101 GTZ Levin Buildup

4AGE Throttlebody Conversion

As you may be aware, one of the most restrictive sections of the 4AGZE intake is the throttlebody. At only 50mm in diameter, it is quite smaller than 4AGE throttlebody's 55mm diameter. The rest of the intake system is about 55mm or so, so I decided it would be a good idea to have a go at installing the 4AGE throttlebody on my car.

You can see the difference here. The 4AGZE throttlebody is on the left, the 4AGE throttlebody on the right. The difference of 5mm in diameter may seem small, but it equates to a decent 17% increase in area.

This mod should take about a day if you've got everything on hand. I still have to work out the idle up for the aircon etc, depending on how it is achieved. I am currently reverse engineering the 4AGZE idle up solenoid and will hopefully have some sort of substitute woked out, most probably with a simple solenoid valve of some sort.

Parts you will need to complete this mod:

4AGE smallport throttlebody
Gasket sheet
1 meter of 5/16 (8mm) inside diameter hose for coolant lines
1 meter of vac hose for power steering
4x short bolts for 4AGE throttlebody with washers (M8 x 40mm)
2.5" rubber or silicone 90deg elbow
2.5" duct or pipe for intake

Tools you will need:

Pliers
Phillips & Slotted screwdrivers
Die grinder/Dremel/etc
Stanley Blade
Socket set
Feeler Gauges
Hammer
Scissors
Multimeter
Offset screwdrivers

Step 01

First thing is to remove the intake piping, original throttlebody and the alloy J-pipe that runs from the throttlebody to the supercharger.
Now, using the gasket from the 4AGE throttlebody as a guide, trace the size of the hole onto the J-pipe opening where the new throttlebody will sit. Remove the 2 studs as you won't need them anymore. I was able to easily remove them with my pliers.
Take your die grinder/Dremel/whatever you've got, and grind out all the metal to the line until you have a smooth transition to the new throttlebody. Using WD-40 or Inox etc. will help with the removal of alloy if you're using a grinding stone.
You will also have to grind a little off the side of the J-pipe to clear the bracket for the throttle cable. Line up the throttlebody on the J-pipe and you'll see where it has to be taken from.

You can see where the metal was taken from in the pictures above. If you take a little too much, it doesn't really matter. You just don't want the air to be hitting a ledge.

Step 02

Now it's time to modify the throttlebody.

First of all, mark a line on the throttle position sensor (TPS) to the throttlebody, so you know how it was exactly positioned. Now, remove it and turn it 180deg. This will allow it to clear the ABV on the J-pipe.
What you need to do is make sure that the TPS has been turned exactly 180deg. By feeling how much deflection the tabs make when it's in its stock location and copying that to the new location you should be able to get it pretty close. Don't worry about it being a little out, we'll adjust it perfectly in a sec.
Now, remove the throttle cable bracket from the 4AGZE throttlebody and swap it with the one on the 4AGE throttlebody.

You should now have something that looks like this..

If you try to install the 4AGE throttlebody now, you'll find that one of the vacuum line fittings foules on the intake piping from the intercooler.
Take your pliers and grab that fitting on the bottom right in the above picture. Now give it a twist and pull out with a twisting motion. It should come out with a little force.
On the 4AGZE throttlebody, you'll see the same fitting in about the same location, except that this one is shorter. You have to remove this one and stick it in the 4AGE throttlebody in place of the one you just removed. The one on the 4AGZE throttlebody is a little trickier, but I managed it by levering it with a screwdriver then pulling and twisting with pliers. Just tap it into place with a hammer.

This is the fitting installed. You can see how tight it is, there's only 1 or 2 mm clearance there. I tried to grind down the old fitting, but it's way too long and simply wouldn't fit.

The next thing to do is replace the gasket for the cold start valve.

Unscrew the 5 screws holding it to the side of the throttlebody and remove the valve. Clean the old gasket off and remove the old O-ring. Give the whole thing a clean and cut out a square of gasket paper. Put the gasket paper over the valve, mark out the hole that's required for the cooland fitting and cut out. A hole punch would be good here, but a sharp blade will do.
Reassemble the valve onto the throttlebody with the gasket paper between. Use a thin phillips screwdriver to punch the holes for the screws and screw it together really tight. Trim the excess with the Stanley blade and dissasemble.
You'll notice that the pattern for the gasket has been compressed into the gasket paper. Using the blade and scissors, cut out the shape. you dont have to be exact on the insides, just make the holes as large as possible without tearing the paper.
Reassemble the valve to the throttlebody with the new gasket, and you're done.

Step 03

Time to adjust the TPS..

Make sure you have the TPS connector disconnected.
Insert a feeler gauge between the throttle stop screw and stop lever.
Using the multimeter, measure the resistances between the pins in the TPS as per the table in the pictures below.

Step 04

Now to fit the throttlebody.

Reinstall the J-pipe to the supercharger. Make sure you reinstall all the hoses and vac lines correctly.
Put the throttlebody in place and use the shorter bolts (M8 x 40mm, plus washers) to secure it to the J-pipe. Don't forget the gasket. Use the one to suit the 4AGE throttlebody, otherwise you'll have to cut the hole in the 4AGZE gasket bigger to suit.

To get the cold start function working, you'll have to extend the coolant hoses by a few inches. Remove the existing hoses and keep the clips. It's a bit tight, but there is just enough room to maneuver a pair of pliers in to squeeze the clips open.
Measure enough of the 5/16" hose (I used some transmission oil cooler hose I had laying around) to run from the engine to the throttlebody and install with the original clips. It doesn't really matter which way around they go, as the coolant just flows through and warms the wax slug that operated the valve.

Now for the power steering lines. They will have to be extended too. I just used some silicone hose I had laying around, but rubber is fine. these ones go to two of the pipes sticking straight up whith the third just blocked off.
Have a look at what I've done in the pictures and follow suit. I don't think it really matters which way around they go, I'll update if I find out otherwise..

Connect the other vac lines as per normal, the positions pretty much line up with the old ones. Make sure there aren't any loose. You'll find two without anywhere to go, these are the positive crankcase ventilation (PCV) pipe and another line. Leave those for now, we'll deal with them later.
Connect the throttle cable to the bracket and test for correct operation. You'll notice that the bracket is offset slightly from the cable. All you have to do to fix this, is slightly bent the bracket that holds the cable towards the throttlebody, and slightly bend out the groove that the cable runs in on the bracket on the throttlebody.
Adjust as required to achieve smooth operation and full throttle.

Install the intake piping except for the alloy piece that was bolted to the top of the old throttle body. Instead you will have to install the silicone bend. You will also have to connect the PCV and the other line into the pipe somewhere before the throttlebody.
The PCV line is where an oil catch can goes if installed, so now would be a good time to install one. The lines can be attached through the bend with some sort of plastic fitting or to the straight section that is needed to connect the bend to the pipe coming from the airbox.
I'll add some more detail here once I've finished this.

Step 05

Adjusting Idle.

This is where you really NEED either an offset screwdriver or a flexible shaft screwdriver.
Because of the location of the idle speed adjustment screw, you can't get a normal screwdriver in, as the intake manifold etc is in the way. Head down to your local auto parts place and get one of these, it'll make your life so much easier.