1998 Expedition 4.6L, 250,000mi

RUNS FINE either after stall/restart (rpms goto 1400 and settle down normally) or by holding gas pedal and keeping rpms above 1200 for 2 minutes.

mechanic wants to start with cleaning throttle body, but is not sure that will correct problem.... does not sound like throttle body problem ( although couldnt hurt with such high miles) [mech has not put it on code reader]

Where to start?
check engine light is on, but its on pretty constantly for 4 years.

which code readers are compatible with the 1998 Expedition?

 

Any standard OBD2 code reader will work. You need to read them out first before throwing parts at it. Parts stores except in CA and HI will read them free, post the exact numeric codes.

 

I'll head to the auto parts store on my next day off and post the codes.

I read somewhere that the cars before a certain date need an adapter for the ODB2. My specific question would be --- is this true and what is the adapter config?

Looking at this:
Also the car has been in and out of the shop 5 times and they never solve the "check engine" light. We just resigned ourselves that its the gas cap or fuel tank pressure sensor-- not going to replace that

 

Okay Error code is P0174 too lean on bank 2... any suggestions since its only on bank 2?

 

Check for vacuum leaks, especially the PCV elbow behind the intake. It rots, splits, and gets mushy after a while. Also, an exhaust leak upstream from the O2 can cause a lean code, you have the EGR pipe on that side that can rot out - but that should also throw a P0401.