How does the idle adjustment screw work??
 

Hey guys, interesting questions... or so I think. I have my car running with MS2 and EDIS 6 and its silky smooth. The problem is that it can't hold idle because it's too low.

I figure the idle adjustment screw works by opening a valve and letting extra air in. My question is which nipple on the throttle body does this air come from? Any of them? Does it simply draw air past the butterfly in the throttle body and not from the external nipples?

- The reason I ask is that I have all the vacuum ports capped off except the one all the way on the back. I'm using that for the Megasquirt MAP sensor. Do I need to uncap any of them or relocate the MAP vacuum line? I have not messed with the screw for fear of messing up the MAP signal to the MS2.

Car is a 1980 911SC.

Hello - I was able to find 2 earlier threads where the idle adjustment is discussed - hope this helps you a bit.

http://forums.pelicanparts.com/porsche-911-technical-forum/418230-idle-adjustment-questions.html

http://forums.pelicanparts.com/porsche-911-technical-forum/740130-idle-adjustment-screw-what-tool.html

Unfortunately, neither of those help with my situation.

to help you would be the best if you take some picture what exactly you have capped or not.
BTW How is you distributor timing?When was the last time you have checked it?

Ivan

There is no distributor, there is no CIS. Everything is capped except for the rear most vacuum nipple. That is being used for MS2.

ok never mind but picture will help;-)
ivan

The idle uses a tunnel between a port above the butterfly and one below the butterfly, with the idle screw as a valve. So, the air is contained within the throttle body, no exterior ports needed.

IIRC the 1980 throttle body has it internal to the housing, while the later 81-83 throttle body has it as a kind of tube going out of the housing.

http://forums.pelicanparts.com/porsche-911-technical-forum/113610-vacuum-source-1980-sc.html

that thread shows the hidden internal tunnel and the idle screw in the first picture.

Thank you, that was the answer I was looking for!

You can also adjust the base throttle blade position as well if the idle screw does not get you where you need to be:

http://forums.pelicanparts.com/uploa...1517610778.jpg