Sudden sooty plugs

[Cherokeedad2]

The 98 4.0 suddenly started running rough and wouldn't idle/ it would die
Like, went to the store, ran fine. Came out, issues
As this seemed to be ignition issue, checked the cap and rotor, fairly burnt, so replaced
No change
Pulled the plugs and they're all black, cleaned and reinstalled, it would idle, but still rough.
Tried a test drive, went 1/2 miles and it died.
Limped it back, no idle again
It's leaving a sooty patch on the driveway

I thought that maybe the cold start enrichener is somehow engaged, but this is happening very fast

Any ideas?
No CEL

 

[Tim_MN]

First thing is to check for active or pending OBD-II Trouble Codes.

Basic rich running should make you suspect the O2 sensors, an exhaust manifold leak, or faulty fuel injectors. Test the Throttle Position Sensor and the Coolant Temperature Sensor.