84 Monte Dieseling 'Erratic Idle'

[84'MC305]

I know the main reason a car diesels is because of the idle, but my car has an erratic idle. Ie, sometimes it idles high sometimes it idles normal. So my bro rotated the distributor to lower idle and I started using premium fuel and it fixed the dieseling problem but I need help on the idling problem. What could be causing this??? Also my exhaust shop said I had a bad sensor because one of my catalyctic convertors was glowing. What sensor could cause this? Any help is appreciated. Thanks

[molehole]

Check Engine Light on? Could be an Oxygen sensor but I don't know if they had them in 84. Check to make sure the idle stop solenoid on the carbureator is popped out when the key is turned on and popped in when the key is turned off. It will stop dieseling and make it idle at a rate that you set at using the idle screw on the throttle cable. BTW the Idle stop solenoid is in front of the throttle cable and looks like a cylinder with a plunger coming out of it. Also try running some carb cleaner through your next tank of gas and also cleaning the carbureator with carb cleaner. It may just be really gummed up. You may want to rotate the distributor back to where it would be stock and adjust everything from there. That is why you have to use premium gas. If the idle stop solenoid isn't working properly your idle gets messed up and it will diesel when you shut it off. Best of Luck