The 3.0L has a crab cap! The inner rotor terminals are rerouted in the cap and appear at different external plug wire terminals. Caps fail, and plug wires can easily be at wrong locations unless you follow manual.
The distributor uses a fine pitch optical encoder, dirt or age may lead to problems with it.
As already listed, the valve guides drop, and they can keep the valves from seating closed. Head gaskets often fail at about 70K miles.
There is also a way to cycle ignition key to read ECU fault codes, 5 - 5 is no codes. The MIL blinks followed by pause, then next number of blinks.
Also timing belts need regular maintenance.
Even with all these issues they were a great running engine, with a consistent 25 mpg in a minivan, with the ability to easily light up the tires.
