Fuel/air mix with rough idle 1990 240

[kylelarsen143]

Hello friends-

A 240 white belt here has been unsuccesfully trying to find the culprit behind a very rough idle. I began the quest of trying to clear the lamda codes for fuel economy by replacing the MAF about four years ago. So far, so good. On my way home from a road trip, I noticed mileage between fill ups diving and started smelling the tell tale signs of burning fuel. I began my attempt at a remedy by replacing old sensors piece by piece, starting with the knock, crankshaft position and O2. That helped for a little while, but after a few months the problem seemed worse than before and I got the code for the ECT. I replaced that, along with the flame trap, thinking "what a clever guy I am" which was clearly my undoing. Somehow I am still getting the ECT code along with rough idle and lean (?) mix under load. It did feel like it was trying to stall a bit on the test drive.

Any Volvo grandmasters out there have a notion about what on earth I should try next?