What kind of problems would a broken air tube off of catalytic converter cause if any? Someone with knowledge please let me know. Thanks im throwing E49 code is this why? bad gas mileage is this why? This is on a 1990 Sedan Deville

The open air tube will allow un-metered/un-commanded air into the system. That causes the O2 sensor(s) to read a lean fuel mixture, whcih in turn tells the PCM to enrichen the fuel mixture, in an attempt to keep the mixture as close to stoich as possible. This is why your fuel mileage is higher than "normal". It will also eventually damage the cat converter, due to the overly rich mixture.

Don't know the code description off hand...I don't have the info in front of me, but it probably has to do with the O2 sensor(s)...

E49: Air management system fault.
The ECM fails to detect an increase of 15 or more integrator counts when AIR system diverts to exhaust. The ECM is not seeing the added air it expects to see when the AIR is commanded on. This is due to the tube being loose from the cat conv. You'll need to repair the tube to correct the problem.:)

Thank you very much. I plan to just cut the airtube down to size and connect with a rubber hose.