Throttle actuator fault

Can anyone help me please? I have a mk5 golf 2.0 140, been having problems with over boost for some time, this got worse and worse until I gave the waste gate actuator a bit of a wiggle, it did make a difference! The only problems I then had was at high speed it would go into limp mode with a fault code of 16618 showing. I guess ive just ignored this problem until my car went away for some bodywork and when it returned I had hesitation and stalling at low speed, could barely get to the end of the road! Had a chap round and found a new code for throttle sensor, now I got a new throttle assembly from vw but this made no difference! Had the AA out last night and they found a code of 5523055 ( throttle actuator ) , he thinks it may be a faulty ECU?

Im really at a loss " help please"

Limp mode. Follow the link in my signature to properly diagnose.

Thanks , Will take a look