Mondv6

Hi all.
I'm new here so hoping I've posted in the right place?
I have a mk3 mondeo 2.5 v6 with a couple of problems I just can't get my head round,
1st one is engine management light has come on, had it plugged in by a mechanic and he tells me it's come up with two codes
1st one was inlet manifold module
2nd catalytic converter.
I've done some digging regarding inlet manifold flaps, as I can see they are a common problem, and they are all in place and healthy! I've tested the module and seems ok as the flap mechanism seems to be working even when the lights on but does increase fuel consumption. After disconnected the battery the light comes off and car runs normal, sometimes the light stays off for a couple of weeks then comes back on!
So could it be the catalytic converter causing this or the module??

Now the water situation, it seems to lose water but when it's cooled down and I loosen the cap off water gurgles back up? But have noticed a brown colour in the water. but it does'nt smell or feel oily, could it be rusty water from rad? I'm sure there's no air lock as I've no air bubbles!
Sorry for the essay just wanted to get as much info as I know in lol
Any help or advice would be much appreciated
Thanks