We previously had gotten an IAG Performance big throttle body for Project STI, although it was a nice piece it was not exactly user-friendly. You had to get the drive-by-wire throttle stepper motor from an STI with a riveted stepper motor cap, remove it and install it into the IAG big throttle body. Well, our throttle body had a clip-on cap and we attempted to get several throttle bodies from junk yards, we failed, always getting clipped on covers even though we communicated well and sent pictures of what we wanted. Junkyard employees just didn’t get it or understand what we were saying and even didn’t get the pictures. It turns out that the riveted covers are rare on older STI’s and more common on 2007 and newer ones so, after our third attempt, we finally got the right part. We didn’t buy a new throttle body because they are expensive and there is no way to tell what you are getting because they all have the same part number!
Here is our IAG big throttle body, it is 76mm vs the stock 60mm. IAG also makes an 82mm throttle body but it is too big for the OEM ECU to properly control the idle speed so it is only recommended if you are going to use an aftermarket stand-alone ECU. You can see the open area where you need to add your stepper motor and cover.
Once you get your stepper motor, you may have to slightly open up the bottom of the well for it in the throttle body casting to get it to fit all the way down. It’s a tight fit and some stepper motors are slightly too big. In that case, you need to be extremely careful because the casting is very thin in that area and it’s easy to break through. In our case, it took a month to find the right stepper motor and cover (for some reason the clipped-covered stepper motors are like 10x more common in the used market!), modify the throttle body casting and put it all together.
To make it a lot easier for those of us who have clipped stepper motor covers, IAG is not selling big throttle bodies with the proper stepper motor installed. These are 100 percent plug-and-play ready to go. You will have to work with your tuner a bit to get the idle right but this saves a long time trying to scrounge up the right used part!