I used to always adjust the Pontiac Varijet and my old mopars. Be sure to count the number of turns you make with the screwdriver so you can always put it back if you want. I think there were 2 screws that you could adjust, one for vacuum and the other speed. there were some other factory "plugged" adjuster screws but like Stoney said they might be sealed. Sometimes putting it on the "scope" doesn't get a good setting so you sometimes have to get the factory plugs drilled out and then you have more room for precise adjustment......on a scope, the mechanic can adjust more accurately for vacuum and speed together as opposed to just turning up the speed.
The vacuum screw might not be sealed, so count the turns and if the idle speed doesn't increase with several turns, put it back to the where it was and try the other screw (if there are 2 on a Quadrajet) because I wouldn't want to mess with the vacuum until you try the idle speed screw.
you could try turning it up a couple turns and listen for a faster idle, then leave it there for a while and make sure it doesn't stall or anything. I had mine turned up enough to idle at 15 kph w/o touching the gas, LOL!
How is the choke thermostat coil??? They do get weak and it effected my idle speed and caused the car to stall because the choke wouldn't open enough and it didn't get enough air, only more fuel. Does it idle fast when initially started, and then get slower idle, as it should? Sometimes you have to "kick them down" or you risk damage to your waterpump. I ended up installing a manual choke for 10 bucks on the Poncho and I couldn't have been happier....
