Hello.  Having problems getting the Zuk to pass smog because it won't idle under 1200 rpm.   Here is what I've done so far - cause it was cheap and easy:
New fuel filter, new plug wires, new plugs, new distributor cap, new ignition rotor, new vacuum lines, new carburetor bottom gaskets at the intake manifold, adjusted valve lash -- still same symptoms.  It runs great under power and will idle all day at 1500rpm.  As soon as I try to dial back the rpm using the the idle screw, it will die.  Also of note is that when I pulled the old spark plugs out, they had a little bit of clumpy white crud on the tips (burning oil from piston rings or valves).
Today after replacing the bottom carb gasket  trying to eliminate any trace vacuum leaks, I decided to mess with the air mixture screw and I noticed something odd. 

The screw has absolutely no effect. All the way in, all the way out -- the engine runs exactly the same.  Is there some gasket around the needle that I need to replace?  Registration is due at the end of the month and I can't get the dang thing to idle low enough to pass smog  AAAArgh.

Thanks for any insight.

Mat (Las Vegas, NV)

Update: More Info.   

Took off the EGR Valve - and it's all clogged and cruddy looking. I will clean it up and try to get a new gasket.  Not sure if this has anything to do with the idle air mix screw not doing anything.

If the idle air screw doesn't do anything, and the engine dies at lower throttle
angles you have a clogged idle fuel circuit and the carb needs to be cleaned.

It could be as easy as a little water or a few grains of dirt in that tiny passage,
or you might just need to remove the needle and make sure it's not gummed
up, should be shiny on the end and not dark, clean it if it is with a plastic scrubby
like on a kitchen sponge, not sand paper.

You can also try to use a spray can of carb cleaner that has a spray tube, stick the
tube in the needle hole and blast it to try and clean/dislodge the blockage, if that
doesn't work you will need to take the carb apart to clean it

Good Luck
Wild

are you getting any trouble codes?
the mixture control screw is set at factory. access is blocked w/a pin. after removal of that pin it can be adjusted w/a CO monitor or a duty meter(like a dwell meter?).
also - there is a switch that is activated at idle that tells the computer the throttle position.
plus o2 sensor, temp sensor, ect.
sounds like mabe some junk in the carb. if you are lucky.
the factory manual has tests for those carb. components.......
i recently went through all that(sucessfully).
took a lot of time and head scratching.

No success with just blowing carb cleaner down the mixture screw opening, so I took the carb apart to clean out everything.
Is there supposed to be a jet where I have circled?  Seems like a perfectly good spot for one but nothing is there.

I haven't looked at any trouble codes, replaced the o2 sensor only a few months ago, haven't looked at the temp sensor.

missing jet?

Looks like there is one in there, way down inside

Yup, just making sure there wasn't supposed to be two jets in the hole, but in the blow out diagram on the carb in the field guide there is only the one - thanks.  Unfortunately, I borked something up with the throttle side linkages when putting everything back together.   The clip about the thickness of a paperclip has unwound - and when everything is pulled tight, the top butterfly valve is not closed.

The coolant and EGR/VSV brackets were removed to show a better picture of what I'm talking about.

That top flap is the choke, it should be OK like that, but if not
adjust it closed more when cold, and it should also be all the way
open with the engine at normal operating temp, or you will run rich

Well, I got the carb back together finally after figuring out the choke linkages and seeing where the spring clip is supposed to attach to.   Now I know that crap doesn't have to come off to take the carb apart

The secondary small jets (the deep ones) were too fudged up to take out and clean, so I just sprayed them down and hit it with an air compressor.  As a side note, careful what hole you hit with air or you will chasing tiny little ball bearings and springs around the garage.  Also be careful with the float pins, the first time I put the carb together, the float pin was out of the hole and no fuel was getting to the carb, so I had to take everything apart again and fix it.

Unfortunately, all was for naught.  The stupid thing still doesn't like to idle below 1500 rpm.  I can put it in first gear with my foot on the brake and release the clutch slowly until the rpm drops to around 1000 and it will run.  It is still a little erratic though.

I now think the problem is associated with the EGR system and lack of vacuum at the valve.  When I give the engine gas, the diaphragm on the EGR valve does not move.  If I take a hose and put it on the top port of the EGR valve and blow into it, the diaphragm will move.   The problem is still the same with a new EGR valve. 

I took the EGR valve off and tried to clean the vent port on the intake manifold to the exhaust with a piece of wire, but it had no effect.  I think the next thing I'll do is take off the intake manifold so I can get a better picture of how clogged (if at all) that port really is.

Took off intake and exhaust manifold to clean out the EGR valve path completely - no change.  pbbbth.
Missed the registration/smog date, so the Sammy is just sitting my garage looking all pathetic for now.