Make sure you put the original ECU back in, hope it's not fried-but since your indicator lights are coming on (ecp and check engine), should be ok.

It could be your TB (throttle body)-which will also turn the ecp light on. It should automatically start to adjust after driving/running a bit, or you can do a reset with the VAG COM software. If it's been sitting without power for awhile (or reset due to the reverse jumping), it looses all it's memory and has to re-learn. OR, worse case, the throttle body got fried.

Best bet is to get it scanned with a VAG COM and go front there-it'll tell you which direction to go.