ECU with idling problem

Hello,

I've have a problem similar to other I've found in former posts about
engine throtling up and down and finally staying up 4500 rpm with my
volvo 460 glt 1.800i. It seemed to be a problem with idling motor, the
first time it solved changing idling motor, but two years later it
failed again and the ECU was affected too. Now I must throttle after
startup during a while until car warms.
Volvo mechanic told me that it was caused by alternator sending high
current, I changed alternator but not the ECU cause is a expensive
part.
I've found two second hand ECU from other 460 1800i of the same year,
but the part number isn't the same.
My car has a ECU Siemens Fenix 3B Spi S101-705-112D, and I've found
similar codes that I've found valid in
http://www.atpelectronics.demon.co.uk/Catalogue/volvo.htm#Volvo Engine Management ECU.
The codes are S101-705-111 and S101-705-113C.

Does anybody know If this ECUs are similar enough to replace my
damaged ECU, or some place where I can submit me question?