A few things I´ve seen that gave me some serious grief, where the plug to my MAP was only partially plugged up, it would just up and crap out on occasion. Another was (I think) the five plug connector near the relay block, the female side of the connector (large red wire) was spread a little and would make iffy contact. I just cleaned it and bent the connector together with a really small screwdriver, to make better contact. The cable at the end of fuel rail, where it makes the bend at the back of head, is prone to chaffing and wire fatigue. Sometimes the wires fatugue under the insulation, you can´t see it, but can often feel it by squeezing the wire between your fingers. The harness at the front of the fuel rail, where it continues over the front of the motor and underneath to the knock sensor, engine temp. sensor and 02 sensor. You have to be carefull how this wire/harness is run, or it will cook and may periodically short to the exhaust maifold.
Any kind of oil, can cause connection grief. Oil has a way of creeping into connectors. The ground to the dipstick holder is always worth a look see, as is the head to firewall ground.
Intermittant problems will drive you nuts, I´ve often wished it would crap out all together, it would make troubleshooting the problem much easier.
