I made same experiences like you.
Look here: http://www.altbierbude.de/component/
Basically the cables are to weak for the construction.
Use new ECBs from Fanatec (ca. 20€) for the clutch and the throttle and check ALL cables for the brake pedale including the potentiometer.
If you are liable to solder, change the thin cables against new thicker cables.
And also fix the cables from the small ECB to the aloi lever of the clutch and the throttle with a cable tie ca. 3 cm under the ECB.