I swapped my suspect 563 ecu for a used 937 ecu last night. The car runs fine with the new ecu, but i have noticed that the idle floats around a little bit more with the new ecu.

with the old ecu the idle was generally a pretty solid 750 or 800 rpms. with the new ecu the idle feels smoother, but it bumps around from say 730 to 770 (moves up a little down a little prettuy constantly).

is this likely something in the ecu (i can live with this) or could the old ecu have been compensating for something else. throttle body has been recently cleaned and the most of the ignition system is new.

as i have documented in other posts i have been chasing an intermittent running problem which i believe is in the ecu as when it occurs, turning off the car and immediately restarting fixes the problem and i have changed just abotu everything else.

if I can establish that the problem was the ecu (does not happen with the new one) then i may have one rebuilt as this new one is still about 15 years old.