Originally Posted by J_C
A few things I would try is cleaning the MAF sensor and idle air control valve, and measuring fuel pressure. You might hook a scan tool up and see if there are any ODBII codes and if it is a type that can read live data, whether your fuel trims are good.
I don't know of any particular relay issues that would cause this but you could consult your owners manual and swap any relays applicable to engine running with another of the same type (under hood junction box probably has 2 or more of each type of the most common relays used).
I'd also look around for loose vac lines/leaks, and if nothing else panned out, which start to suspect an intake manifold gasket leak though at some point that ought to show up as rich (positive) fuel trims on a scan tool showing live data.
You did not mention which engine yours has.
I had to clean the sensors on the old honda, air control valve, etc.
I will get under the hood this weekend.
I think I have a vacume/ fuel pressure guage in the shed.
The glove box was empty, no manuals, and no history of maintenance.
I am an aircraft maitenenance technician, and I keep good records on cars.
But this one is new to me... Fords that is, last Ford was a 1968 fast back.
I will post the engine model tomorrow, dark now.
I plan on getting all into the engine compartment this weekend.
I will be buying a factory manual, and wiring harness book.
Going to auto zone or O'rileys to see if they can check the codes.
I know the O2 sensor is bad, but other than that, we will see.
edit.. it is a 4.0 L