crankshaft position sensor

Not familiar with Renault, but the crankshaft position sensor......well, it tells the car's computer the position of the rotating parts of the engine. That lets the computer decide on ignition timing...when to fire the spark plugs. It's possible you made a human error and didn't do a good enough job of soldering the wires the first time.....but I find it hard to beleive that you're getting it wrong every single time....it has to be something else. It might just be that you're either unplugging the sensor or disconnecting the battery every time you go to resolder these connections? Try just disconnecting the battery for a few minutes, reconnecting it, and see if the car again drives better for a few weeks. If it does, you know it's not your soldering job. Either you've bought an incorrect sensor, or something else is wrong with the car.