26 February, 2005
|The throttle body was next. Because the TEC│ will use its
own Idle Air Control Valve (IACV) circuit for controlling idle, I had to
make a modification to the stock IACV, which attaches to the bottom of the
The modification will keep the stock IACV in its fully open position, so that the TEC│ IACV can take over its functionality.
|The IACV uses a solenoid to open and close an air valve.
Although the solenoid will be disconnected, its permanent
magnet will be used to keep the air valve in the open position.
First, remove the IACV assembly from the bottom of the throttle body.
|Next, remove the two screws that hold the spring assembly into
|Remove the coil spring and the plastic insert:
|Peer inside the opening and you will see a small arm
attached to the end of a shaft. By rotating the arm with your finger, you
will feel that it will snap into one of two possible positions, as the
solenoid magnet is what keeps it in place. The photos below show
those two positions:
If you turn the IACV over and observe the air valve, you can verify the correct position to keep the valve open.
|Make sure you position the arm in the correct position,
against the stop screw. Discard the plastic insert (or put it aside for
returning the IACV to its stock configuration), as it will not be used.
Reassemble the coil spring assembly. Without the plastic insert to engage
the arm, the magnet on the solenoid will maintain the arm in its correct
|Re-attach the IACV assembly to the throttle body.
most of the throttle body to clean it, and I made the mistake of trying to
remove the two small screws that hold the throttle butterfly in place. As
luck would have it, both of the the heads in these small (M4) screws
stripped right out. To make matters worse, I broke off a small drill bit
trying to drill out one of the screws!
In the end, I was able to get both of the screws out using patience and liberal swearing. However, when I tried to replace these screws, Toyota told me they had no part number listing -- they were only available as part of the entire throttle body.
OK, I thought, I'll just find some M4 screws of the right size and use those. Right. It turns out these screws have a special small head size and even the angle on the head is non-standard.
I tried grinding down the heads on some flat-head screws, but the head crumbled once the slots were reached, regardless whether I used Phillips or slotted screws.
Finally, I located a vendor, Fastener Express, that sells M4 flat-head screws with a hex socket head. These were aluminum, so they would be easy to grind, except for their tiny size. With patience (and more swearing), I finally fabricated replacements for the butterfly screws:
Here's a photo of the cleaned-up throttle body with a new gasket (Toyota Part No.
Installing it is a breeze:
Next comes the throttle body support piece, which Toyota calls the Air
I had a small problem here. This is a '91-92 valve cover, which uses two cylindrical standoffs to support the Air Connector Stay. The bolts are M8, and the thread in the top of the cylinder head is M8, but the spacers are sized smaller. I just drilled them out to accept the M8 bolts.
I decided to remove the studs on the Air Connector Stay and use stainless bolts to attach the air horn. With all the components fitting as they should, I torqued down the intake manifold to spec. I then went back and tightened the two long bolts securing the throttle body to the cylinder head.
|I needed to provide the Tial wastegate and the TurboXS blow-off
valve (BOV) with vacuum/boost lines, and Tial recommended that these lines
come from the throttle body but before the throttle butterfly. All
of the existing pressure nipples were located on the intake manifold,
which is after the butterfly.
I decided to tap a couple of ⅛" NPT holes in the base of the throttle body's air horn (Intake Air Connector). There was room to access this location and plenty of material for support:
|With the holes drilled and tapped, I wrapped some Teflon
tape on the threads of a couple
of 45║ ⅛" NPT x ╝" hose barbs and installed them into the air
I then installed the air horn onto the throttle body and tightened down the
|I didn't intend to reconnect the throttle body coolant
lines, so I simply capped off the nipples on the IACV body.