Advised by mechanic to find a working throttle unit from exactly same model year and engine type, then there should be no problem for ECU to control it. I found one with yellow label, which should be the updated type from a car with 200 k miles. Part and CAN-bus number totally different, but works perfect. No stumbling in idle or any hesitations in acceleration. Took 40 min to replace, would have taken 10 was it not for the (with my hands) difficult to pull apart connector. Finally found a suitable screwdriver to both push on locking mechanism in and hold the (seen from front) right-hand connector half, while pulling with left hand on the other. Was for me impossible to stick in both hands at the same time and get a grip on the connector locking mechanism.

Thanks for all advice

Gustaf