I have a 1981 280Zx N/A engine I put into my 1972 240Z. I aslo have added a cold air intake system. I am having erratic idles issues, when idling the tach goes from about 800-1200 back and forth. I also have removed all of the emissions stuff and only have EGR left. I have been reading about vacuum problems and when I remove my oil filler cap the idle doesn't change. I have 3 nipples on my thermal vacuum valve. The rear nipple towards back of engine goes to distributor and tees off to my throttle body on the bottom. The middle nipple goes directly to the throttle valve. The front nipple I have capped off. Does this sound right?

Then on my Weber big throttle body there is a round hole on the top right of the attached picture, does that need to have a hose going from my valve cover to it?

Thanks a lot for any advice.

 

If there is no change when you unscrew the oil cap then You have a vacuum leak some where!!
Check:
PCV valve to the block breather hose.
Valve cover to the AFM boot hose.
EGR base should be pluged if you're not using it.

 

Thanks alot for the places to check. On that note I have a little air filter on my valve cover so no hose to AFM boot. I am not sure if this hole on my Weber throttle body needs to be plugged or better to run hose from valve cover to it?
I have a new picture with a circle around the hole I am referring too on my Weber throttle body.

 

i think that hole was for the idle air bypass, if you cover it with your hand does it feel like it has suction? try opening the throttle a bit if there is none at idle to verify. you can use a piece of aluminum tape temporarily to cover it or a frost plug to seal it properly