Question

I got the engine code P1726 on my 1997 Ford Expedition 5.4L, rough idle on start-up, flashing TCIL

Answer 1

Rough idle on start up and a flashing TCIL, these are 2 separate issue, when there is a flashing TCIL this mean there is no TCC operation either from a transmission that is slipping. Check the transmission fluid condition , The rough idle at start up will not set a P1726 or a P1726 will not cause the rough idle. ignition misfire are most noticeable at cold start up.