What does this do? (Throttle Body related question)

[IronMonkeyL255]

I was checking something near my TB when I got curious.

What does the large screw in a raised portion of the TB do? It's rather wide and has a flathead slot in it. I unscrewed it and cleaned it off before re-installing it. It had what looked like it could have been a petrified o-ring on it, but I wasn't sure if it was that or some other kind of seal, otherwise I would have replaced it.

Anyone know? Did I just kill my car?

[vrg3]

My understanding was that it was some kind of needle valve intended to allow for factory calibration of early throttle bodies' bypass flow. In the middle of 1991 they switched to a differentl throttle body that didn't need it. According to Subaru, you're never supposed to turn that screw.

If you put it back exactly where it was, I guess it would be fine. You probably didn't, though. How does the engine seem to run?

[IronMonkeyL255]

It seems to have fixed my high idling. Instead of ~1000-1200 it's idling closer to ~700-850 out of gear and stopped. I ran it around, and it didn't seem to want to stall.

I could probably back it out some and be good.

[IronMonkeyL255]

Also, do you know if it's supposed to be an o-ring on there?

[entirelyturbo]

Also, do you know if it's supposed to be an o-ring on there?

My diagrams show me no individual parts in that area. You can't even get the screw itself.

As Vikash said though, you're not supposed to touch it, like all the rest of the screws on the TB. Technically, if you wanna follow Subaru's advice: Remove that throttle body and discard it. You need a different one now

The TB, in my honest opinion, is a non-serviceable part. You can get away with TPS maintenance if you closely pay attention to the original location, but that's about it.

[IronMonkeyL255]

Eh.....

Whatever. I think my TPS may be acting up anyway. I'll try driving it around for a while anyway. If I start getting 2 mpg or something else bad, I know I've really screwed something up.

What shocked me is the fact that I could turn that screw with just my finger. I actually unscrewed it with my thumbnail it was so loose. I doubt it's been in the factory position for a very long time now.

[IronMonkeyL255]

After much thought and consideration, I believe there was an o-ring there. Likely the heat made it petrify, and this caused there to be enough slack that the screw backed itself out.

I'm gonna replace the o-ring and adjust it for a slightly higher idle.

[vrg3]

Hm, interesting. It makes sense that there would have been something in there to seal. Like Michael says, Subaru doesn't list any spare parts because you're not supposed to ever take that stuff apart. But if the seal fails, it certainly could cause idling trouble.

Hm. I wonder how many board members this could be affecting.

Maybe you could try swapping to a cheap mid-92-or-later throttle body that didn't use that valve.

[IronMonkeyL255]

I may do that if I can get my hands on one.

It's idling just about perfect now that I replaced that and backed it off some (not even a full turn).