1500S

That factory service manual is exactally what I was looking for, thanks!

And yeah, I'm reasonably sure it's the choke. When it happens, I have to pull over and pop it loose with a really long screwdriver.

Looking at the factory service manual, I can see that the automatic choke is controlled by electric heater circuits (if I'm reading it properly). Could it be an electrical problem? This car has a ton of those (radiator fan doesn't work automatically, running and dash lights don't always come on, sometimes car will fail to idle if the heater fan is turned off, heater fan doesn't come on until number 2 setting, etc...). Also, what would be the 'right' way to disable the choke completely until I can get the problem properly fixed?