D15B4 - Whats this do?

[90civicGL]

Ok, so basically my engine is idling at a high RPM (2000ish) and when we push this mechanism down the idle drops to something closer to normal (750-1000). Although there is nothing connected physically that I can see that controls this... how does it work and how can we adjust it?

I have some pictures of the mechanism from my spare intake assembly.

https://dl.dropbox.com/u/31202161/pushthing.jpg
https://dl.dropbox.com/u/31202161/pushthing2.jpg

Also, what is the function of this and what does adjustment of the screw do?
https://dl.dropbox.com/u/31202161/top_thing.JPG

[tiksie]

There's an idle adjust screw. Follow the accelerator cable to where it ends.

Find it.

Screw anti-clockwise until you get desired RPM.

Leave it alone.

Done.

[ECU-MAN]

looks like the choke mechanism

[tiksie]

looks like the choke mechanism

Correct as per usual, good sir. Mechanical cold start haha.

[90civicGL]

That was my understanding of it, but I was confused because I have been told by mechanics that the choke can not be replaced in these engines. Holding the level/pushing the rod going into the black box (choke?) does fix my idle issue, and if I push it in as far as it goes then the car starts to stall.

So I am assuming there is something wrong with either vaccume hose 18 or 28? We have tried attaching a syringe to both 18 and 28 and push/suck air through them but nothing seems to push the rod in and out adjusting the lever thing circled in red above. (the thing circled in red seems to open up the butterfly valves in the carb to let air in through the intake.

I have tried adjusting the idle screw but it doesn't seem to be affecting the idle speed. So I am guessing there is over fueling going on. As black smoke also comes out when releasing the throttle after going to a high RPM.

Another indication of over fueling is that when I turn the car off the engine keeps trying to run for 3-8 seconds burning the left over fuel. not run like normal but just sounds as if it was trying to turn over.