Furnace Short-Cycling

I took the furnace apart in order to look at the burner. Everything, including burner is clean (as it should be, it's only 2 years old). I did notice a couple grains of debris (the size of grains of sand) in the screen filter in the gas line right where it connects to the main gas hose. I cleaned out the debris, put everything back together and it's working as normal, even with the restrictor piece inside the exhaust vent. However, I'm not convinced the problem won't return since it has worked for short periods of time recently.