Those are generic error codes. From a multi make reader. Enthusiasts tend to talk in BMW specific codes as they are more specific. Pulled using a BMW reader (good news is they are cheap enough if you decide to get one). So we'll be a little less familiar with those codes on here and the advice will consequently be more generic.
P1619 is generally associated with the thermostat. Possibly a failed temperature sender. But what it specifically means on a Z3 I don't know.
The P0155 is as it says generically associated with an O2 sensor. But from experience O2 sensor codes on Z3s are set frequently from intake leaks in rotted rubber pipework. I also have my suspicions the P1619 might even be caused by the same thing. This would be consistent with going nowhere and a fault suddenly appearing. Changes in temperature, rubber rotting past point of air tightness etc.
Anyway, as Tony says, important to clear the codes first. And try again, especially given work has recently been carried out.
PS - would give your post title a bit more detail rather than just 'Z3' then it will help attract those who may have suggestions to make.
