Nervous engine tick during idle after rebuild

I recently rebuilt my 1991 Nissan 240sx KA24DE engine. New piston rings, valve seals, rebuilt head, cleaned and hot tanked block; all new gaskets, filters, timing chain, water pump, spark plugs and distributor.

When I start the engine, it fires up, but the engine seems to shake side to side every few revolutions like it has a nervous tick, enough to make the front end shake slightly. The engine mounts are in good shape and were inspected before reinstall of engine.

If I rev it above 1000rpm it seems to go away, but it will not idle smoothly at 700 rpm which is stock idle. If the engine warms up it is not as apparent but is still there. The car is timed properly and will drive without a problem

I did not replace the fuel injectors when I rebuilt the engine and the car has 190,000 miles. Could this have to do with it, or is there something else I might have missed?

Any thoughts or suggestions would be helpful as I dont want to be causing any damage to my car.

The possibilities are many. If the engine movement is caused by a misfire, the causes could be: vacuum leak, EGR leak, dirty injector, ignition fault. If those engine mounts are 18 years old and have 190K on them I would replace them no matter what they looked like.