My LG4 IROC has been sitting for a while and the engine is running a little rough. Do additives such as STP carb cleaner or gas treatment really work?

 

You probably have bad gas. Just pour in a little fuel stabilizer next time you store your car.

Change the oil, use a whole quart of Marvel mystery oil with your regular oil (don't overfill)

Pour about a half quart of Marvel Mystery oil and a few ounces of B-12 chemtool at the pump before filling up. (don't get that stuff on the paint)

Drive the car on a long trip on the freeway, burn through that entire tank of gas and refill it agian with the rest of the B-12, use the rest of the Mystery oil if you want too. change the fuel filter. Open her up a couple of times and keep driving it. it will be fine, trust me.

As far as STP or any of that other crap, it's a waste of money.

I did use Duralube fuel additive in my Corolla one time, it worked very well, but I haven't been able to find it.