Hi
Sorry to hear that your car has been out of action for so long. I'm sure you've been given the run around, some repairers will tell you anything (when they really don't know themselves). As others have mentioned here the obvious things that came to mind were a bad or reversed connection on the throttle pedal (but that won't generate a check engine light) or something going on between the ECU and the throttle body, ie. bad connection or wiring short (that might generate an error code). If you find a wiring short your ECU might still be OK. Knowing the actual error codes would really help a lot, but if a repairer has read them before then they've probably also erased them.
You must make sure that you get your original ECU back from the repairer as it contains all the information that matches up to the immobilizer (skreem module) in your car. It's much easier to make a new ECU if you've got the original ECU to copy.
I wouldn't normally expect an ECU to fail, but it could happen. My main concern would be that whatever caused the ECU to fail (eg. a short in the engine wiring harness) might still be present and cause the same failure in any replacement ECU. It would be very odd for the ECU fail all by itself. So check this out before you plug another one in.
However, to answer your original question, yes your original ECU can be easily duplicated using a used ECU from the wreckers. You wont need a new ignition, keys or skreem module. The best ECU to use would be one from another manual transmission Crossfire.
If you have a reputable electronic repair shop near you, take the ECU's to them and show them these instructions.
1. Unscrew the cover from the ECU.
2. Lift off the lid from the bottom casing.
Note. the rear edges of the circuit board are glued to the lid with mastic and we need to get at the rear of the circuit board.
3. Run a Stanley knife between the circuit board and the lid to separate them.
4. The 5P08C Eprom circled in Red contains all the vehicle ID data and coding. Pin 1 of the Eprom is marked in yellow. We want to copy this chip!
5. Connect an Eprom Reader/Programer to the 5P08C on the Original ECU and read the binary file from it (and save it on a USB for future use).
6. Dissemble the donor ECU as described above, connect the Eprom Reader/Programer to it and write your original binary file to it (the one you just copied from your original ECU).
7. Reassemble the ECU (you don't need to apply new mastic), fit it to your car and start your engine!
If the repairer doesn't have a suitable in-circuit programmer then they could carefully de-solder your original Eprom and fit it to your donor ECU.
I hope this works for you out and you get to drive your car again soon. If you don't have the original ECU, then you'll need to buy a new one (or virginise a used one) and marry it to your vehicle using Mercedes STAR DAS (Xentry) software.
If anyone else ever wants any advice regarding Crossfire ECU coding or modification then please PM me and I'd be happy to help out.
Pic 1: Crossfire ECU
Pic 2: ECU with Cover Removed
Pic 3: ECU Circuit Board Separated from Top Cover
Pic 4: 5P08C Eprom on Bosch ME28 ECU
Pic 5: 5P08C Eprom hooked up to Reader/Programmer