Inspect the convoluted hose that attaches to the left side of the airflow meter, and the short straight hose that is clamped onto the throttle body.Vacuum leaks at these connections are common, and the airflow meter flap will notopen properly if the leak is severe enough.

High mileage 4.2 engines occasionally suffer fuel pressure regulator failures that result in excessive pressure: your pump is working, but if the regulator is stuck closed, theplugs are getting flooded. You need to connect a pressure gauge and see what is in the rail when you crank it over.

Listen for injectors clicking when you crank the engine: a failed coolant temperature sensor for the fuel injection will disable the system, so proper fuel pressure does you no good if the injectors aren't opening to fuel the cylinders.

If any of these points are helpful, please let me know what type of doctor you are so that I may get somefree advice in return. Hopefully you are in the mental health field.

 

Listen to the injectors with a stethoscope (or through a screwdriver handle, since you're no Dr.). Coolant sensor for injection is on RH side of engine, atop water rail, towards the rear. Buy a Haynes manual for $15.00 and try to keep the pages clean.

 

I had a similar problem recently turned out to be a bad wire in the cold start circuit I believe it was near the "thermotine" switch. Check your wires and relay connections.

 

Thermotime switch opens cold start injector for a max. of 5 seconds: absolutely necessary for cold starting, but irrelevant once engine has started. This would not be associated with the rough running once started, provided the symptoms were accurately described.