Thought I would post it here for future owners. 52k original mile truck that sat for 25 years. Could not get rid of a persistent P1552 code, idle was off a bit too, much too high. Swapped IACV units, checked out the wiring, nothing. Finally swapped the ECU with a spare set I had, that fixed it. 2nd bad ECU I have had, had one a long time ago with a bad oxygen sensor internal circuit. FWIW.

 

Thanks Extinct. Rare but I guess it does happen.