Bucking at 2000rpm, once warm? rough idle? bouncy tach? No codes?
 

This was happening in my 92 lx. You could turn the car on and it would run fine for about 15 minutes then once it warmed up it would start to buck at 1900 rpm til 2500. and running like crap. it turns out it was the pip sensor on the distributor. If you are having similar symptoms, check the pip sensor. Just thought i would pass this along. Good Luck.