Three immediate things to check.
1. Water temperature sensor connection at front of block.
If this is disconnected I believe will make the engine run very rich/rough. The wires on top on the engine get very cooked and vibrated. Injector connections are usually OK.
2. Central ground for white injection system wires toward rear of intake manifold. If you can catch the engine stumbling, work these wires around to see if it corrects. This may require recrimping or soldering the wire connections. Again, subject to heat and vibration.
3. Ignition points, dist cap, rotor. Standard maintenance.

Ther is also the thermal timer switch/cold start injector system, but only if the thing start hard while WARM is this suspect. The throttle switch, the map sensor, and other things are less likely to cause this type of problem. Those would be more severe.