Richard Miller

I'm sorry for such a simple question, yet here I am. I have a S4 throttlebody. In my time with 12a's and carbs the primary had a slight gap for idle.The FC FSM lists a 1.1mm through 1.7mm gap for the primary valve. I had to eyeball the gap ( throttle in closed position) but still had to seat the idle screw in the most closed position. (not torqued but seated) the lowest idle I could get is 900 rpm. and that is the lowest. I have the manifold off and revisiting a few things. Throttle being one of them.

I'm beginning to think that there should be no gap in the primary with the throttle at rest. the set screw is there to keep the throttle plate from hitting the walls of the TB, but thats it. the single hole in the plate and the idle screw bleeds enough air for idle. As this is my first time really working with a throttle body I'm Looking for confirmation.
thank you

WondrousBread

My throttle body was almost certainly messed with before I got the car, so take the following with a grain of salt. I think there should be no gap, and that's what I'm running right now.

The FSM specifies a slight gap, but this is assuming the thermowax is still present and on the "cold" position. It's set using a screw on the back of the throttle body. Basically, this controls the "cold" high idle setting. Once the car becomes warm, the gap closes down and the primary is shut at idle.

I'm not sure how it works on 12As, but S4 throttle bodies have a small screw on top (NA models, TII have it on the BAC valve) that can be used to control bypass air for idle.

j9fd3s

iTrader: (3)

try adjusting it, i'd go in some easy to remember increment, like half turns or something. its best if you can do it with the engine running, although i'm not sure how easy it is to get to the screw(s)

Pete_89T2

iTrader: (4)

The primary throttle gap you're referring to above is measured at the point just when the secondary plates start to crack open - this gap is NOT supposed to be adjusted with the throttle stop screw, but by tweaking the cam adjusting screw on the secondaries shaft as shown in the FSM diagram below. Normally you should never have to mess with this, and unless someone seriously molested your TB, it should never need adjustment. Below is an excerpt from the S5T2 FSM, should be very similar for the S4 NA or T2 - just get the right FSM to verify & follow that.

As for your suspicions that there should be almost no gap with the throttle at rest, you're correct - assuming the engine is at full operating temp and is completely off the fast idle cam (controlled by the thermowax). Basically if your idle is a still a bit too high with the BAC valve disabled, you can use that throttle stop screw to close the throttle a wee bit more if it was cracked open too much to begin with.

FYI, if you have a spare/junk TB laying around to scavenge parts from, the spring loaded TPS adjustment screw can be swapped into the throttle stop screw location. Since there's no jam/lock nut to deal with, the spring loaded screw makes adjustments with the car running infinitely easier with a long enough screwdriver.

Richard Miller

Thank you all who replied . I have the throttle body stripped per the teamFC3s write up. I'm also running a Haltech, so that changes some of the support system needs. I'll go to fully closed but resting on the set screw but notrubbing on the throttle cylinder wall.

thank you once again