Same Issues As me
I got a 2005 156 last week as well. The moment i drove off i got the same error as you. The car felt normal when driving as well but it stalled whenever I slowed down in traffic.
Luckily have got a friend of mine who owns an OBD tester. Result was that the cam sensor was faulty. After replacing it, everything was fine.
Then came another issue where my cabin smells of petrol. Turns out to be a leaking fuel pump at the seals. Which the only option is to replace the pump as I tried using sealant to fill the hole. Off I go tomorrow to get it replaced as well.
Although there is so much hassle in this car, it really brings out a smile whenever i brake into a corner, this car never fails to impress me with its handling.
It's best to get an OBD test to see if there are faults being registered in the ECU.