Sounds like you may have gotten a vacuum leak. As far as idle, if its a carb type car yes very easy to adjust idle. There is an idle screw that you can get to from the drivers side of the carb. Look down on the lower area of the carb behind the linkage a tad. The screw head is in front. It pushes on the linkage plate. you'll find it pretty easy. If your car is injected there should be a similar screw on some kind of throttle valve but I don't know where it is.
Check all your vac hoses that attach to the carb. Power brake hose, vac source for all of your vac operated stuff. Maybe pull then and plug the hose going into the carb to make sure you do not have a vac leak within one of your devices. Other things that can cause loss of idle would be low fuel supply/pressure to your carb. I just replaced the tiny fuel filter that is in the fuel inlet on my 72's carb. It was clogged. I was losing idle speed, had some hesitation on throttle up and hard starting do to fuel starvation. A distrib that has reduced advance will cause slower idle speeds also. Maybe its loose and turned on its own? All easy things to check. Good luck, Dave
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My Christmas present to ME! Bought Sat 11-30-2013. 72, 350 4 spd, Silver with blue interior...Can't you just hear Pablo Cruz playing in the background?