Bmw z4 2.0 almost stall on cold start

[Z4it]

Hello, I'm mirko from Italy. I recently bought a bmw z4 2.0 but this car had some problems. I've already solved almost everything but I still have a couple of problems. Let's try to solve the first one. In cold start the engine turns on immediately but then it is not regular and almost goes off. Then it stabilizes and does not give any functioning problem. With the dis v57 I read the control unit and I had a camshaft sensor error. I replaced them with two magneti marelli sensors, the error went away for some days but the problem persists. Sometimes it appears again, one time cam sensor 1,another time sensor 2. I can read it with Torque for Android. When I wait 3-4 hours after switching off the engine, I have no problem with the ignition. The problem is only with the cold engine. Also cleaned the maf and changed the sparkplugs. Sorry for my English. I hope to solve this. Thank you very much