Check the coil. Should have lo resistance pin to pin on the plug, several 10's of thousands from either pin to the Hi voltage tap.
I have/had the same problem, same symptoms. I awaiting a PCM. The PCM caused the alternator to full field. This gave me 17 volts to the battery, which in turn toasted the coil, among a couple of other things. The key seems to be "low voltage, just barely moving past the 9" reading on voltmeter.
I have yet to measure the field input to the PCM, it is on the list. One side of course is 12 volts, the other, regulated side, should have a hi resistance, I'm expecting to find it shorted. As an aside, I have read, "if you disconnect the plugs on the PCM without disconnecting the black battery, this causes the false data to be written to the uprocessor". This is irreversible.
FWIW this is a 99XJ, 4.0, Auto