Sunder gave some good advice on the sputtering portion of your problem. The most commonly failing sensor that will cause a hesitation is the TPS. Moisture can penetrate the seals and cause faulty, yet plauseable readings that may or may not throw a TPS code.

Did you have a chance to check for any stored codes? If you have any TPS/MAP rationality faults stored, a common fault I find with '99 TJ's is that the 5V power supply to both these sensors also powers the speed control switch pod in the steering wheel. The clockspring for the airbag and horn wiring also carries wiring for the speed control switches, even it your TJ doesn't have speed control. The clockspring shorts out the 5V to ground and the sensors loose their power supply. A simple test is to unplug the black wire connector for the clockspring and see if the fault goes away. (Note: Don't unplug the yellow connector, on the clockspring, it is for the air bag) You will need to remove the lower steering column cover half to access the connector. If the fault comes right back when you reconnect the connector, replace the clockspring.

Here's one method of testing the TPS without a scan tool:

If you have a digital multimeter you can backprobe the TPS connector's center terminal (orange with a dark blue striped wire) and check the sensor return voltage at idle (closed throttle). It should be steady, Minimum volts is .26 Volt, max is .95 Volt, normally, it's between about .65V to about .80 volt DC. With the throttle closed, the voltage should not change with the engine at idle. With the engine turned off, key on, the voltage reading should smoothly climb as you open the throttle wide slowly by hand to around 4 volts or so. The volts at WOT should never be over 4.49 Volts DC. The other two wires in the connector are the 5V feed and the ground. If the voltage on the sensor output circuit are off, check for voltage drop and continuity to the battery ground from the brown/yellow stripe wire, the orange wire should have 5V on it with the key on. If you have a good ground, with no 5 Volt reference, suspect the clockspring as described above.

If the voltage on the sensor return circuit reads something like 1.5V at idle and/or skips around as you sweep the throttle, replace the TPS.

Like Big Jim said, most likely you have a seeping freeze plug causing the coolant smell and leak. Hopefully, that's all it is!