e46 316i 1.9 engine - P0171 code

[philgw100]

I have a 2000 316i that sounds like an exhaust manifold blow, but it is not, also comes up with a P0171 code. on initial start up for the day this sound (Like an exhaust manifold leak)occurs then its OK for the rest of the day. I have checked inlet pipes as best as possible and renewed the bolts that clamp the secondary air pump together. I then held outlet pipe from secondary pump and when i lightly blipped the throttle could feel the blow through the pipe. I then disconnected the inlet pipe to the secondary air pump to check for vacuum, which there was. On blocking off the the intake the noise went.
This noise only occurs on 1st start of the day, when checking for vacuum at secondary air pump on subsequent starts there is no vacuum and pump does not sound like its running.

1 - is it normal for pump to only run on 1st start
2 - could this just be a sticking relay (but strange it only ever does it on 1st start of the day)
3 - is it the valve on rocker cover that opens and shuts feed to exhaust (if so could this be sticking open and allowing exhaust gasses to come back throught the system)

Thanks in advance