87 sammy, stock everything.

It ran fine when last driven (about 2 weeks ago), and was idling great when parked.  Today, it wont idle at all.  Start it up, it'll run as long as you hold your foot on the gas pedal, as soon as you stop it dies instantly. 

Replaced the following today:  plugs, wires and fuel filter.  Checked the vacuum hoses and all seems fine there.  The only other thing I can think of is the choke, and am going out to check that now.  What else should I be checking??

Choke is working.

I did find that the 5 screws to the top of the carb were loose (the screws that hold to top part of the carb in place).  I got them as tight as i could, and it idled roughly for a few minutes.  I sprayed some carb cleaner on the screws and the idle smoothed right out.  I got the screws as tight as I can but it still wont idle.

wtf??

Had a friend come over and check it out.  The only thing he found was that the carb float was set to high.  We reset that, and it does idle better.  However, the engine is missing bad and still wants to die.

I'm at a loss, cant figure this one out.  How can it go from running great to running like toasted over chit when it wasnt driven or even started?

The only way to go bad that fast would be something electronic
just went bad, so look at any sensors, and look for a bad vacuum
line while you are at it

Wild

you said you replaced the plug wires. double check the firing order. sounds like you have 2 wires reversed.

Had some more time to work on this, havent made much headway.

I managed to get it to at least idle, although very rough.  There is a serious miss somewhere that I cant seem to figure out. 

New plugs and wires (yes the firing order is right) cap and rotor.  Checked vacuum lines and sensors, all seem fine as far as I can tell.  That really only leaves the distributor and coil as possible causes.  Someone suggested to look into the pickup coil as a possible cause.  Anyone got any other suggestions?

Found the problem.  Somehow, the timing jumped from 10 BTC to about 15-20 advanced.  Reset it to factory specs, now just gotta get the carb reset and idling right.

Updating for anyone who cares (or for future search help).  Took it in to have the carb dialed in, and found that i have what the mechanic termed a 'massive vacuum leak' at the base of the carb.  Did some research, came to the realization that there are supposed to be gaskets on both sides of the carb baseplate and I didnt put any gaskets on last year when I replaced the carb.

Sooooooo, called trail tough and ordered the gaskets.  Will update again when warranted.

Well at least you found it, that makes sense now that you found it

Update:  The gaskets helped, but it still wasnt running right.  My mechanic did a smoke test on it, and found smoke coming from the throttle plate area.  Seems the throttle body bushing is bad, which the company who I got the 'remanufactured' carb from last year swears they changed.  Sure ya did.

Anyway, removed the carb and took it to the shop for repair.  Still waiting to hear what all is wrong with it, but they did say that the idle solenoid was bad also. 

I hate those dirt bag shops that lie to you about the work they did 

I don't trust anyone to work on my stuff for that reason

Wild

No doubt.  When I told them, they said "Oh, we changed it.....but send it in and we'll change it again for $85."

No thanks

Why would the timing jump 5-10 degrees? The reason I ask is because my 86 Sami did the same thing last week. I was just pulling into work and suddenly it started missing and ran like crap. Thought it was the fuel pump because I choked it (manual) and it hobbled into work. But what I found was the timing jumped just like yours. The hold down bolt was tight so I don't think the dizzy moved.
Sorry about the hi-jack..
Bob

The last time I had the timing moving was the belt on an Audi
that was starting to go, I scratched my head trying to figure it
out, then the belt lost a bunch of teeth in 1 spot, and I figured
it out, changed the belt.

Wild

I've been wondering about this myself, and Wild just about has me convinced to change the belt.  I already have a new one, why take a chance?

I did take the timing belt cover off and check it while trying to figure all of this out.  It appeared to be ok, no teeth were missing anway.  My gut told me to change it then, but I didnt because I had never done one before.