New problem need help

[RangerJ]

1989 4x4 xlt 2.9 auto.Well it ran good for a few days but now another issue, while sitting in line at the bank drive thru the engine idled down to around 500 rpms and the oil pressure gauge dropped to nothing, I revved it up and the op rose to normal while this was going on the tach was also jumping up and down.I replaced the op sending switch approx 3 years ago,I guess its time for a new one. I have had this loping idle before thought it was fixed.Could it be electrical problem somewhere? Anyway I need the advice of this site once again. Btw after letting it sit about 30 minutes the loping did not return.There are no additional engine noises.

 

[IMenriched]

Might be the TFI or ignition module...starting to go. remove and test

have checked for codes??