So, my girlfiend's 2005 A4 has been acting strange lately. She went and had the 75K service done a month or so ago and now has 78K on it. There are a few issues that the car is having.

The first one is is that the coolant level is really low. I'm at work but she said it's probably around 1 inch below the MIN mark. This was first thing this morning when the car was cold.

The second issue is she is getting horrible mileage now. I replaced the fuel filter thinking it would help since it's never been change. I am 99% sure it's on correctly and the hoses are connected correct. But, what would happen if they were not connected correctly? I took them off one and a time and connected them to the new filter so I made sure they were correct. There are no signs on fuel anywhere under the car after sitting, ect.

The third issue is that when she started the car this morning, she noticed that it was shaking pretty bad. She got out and popped the hood and could se the engine visibly shaking.

Any ideas on the issues/problems? It has the 1.8T and is an auto. The car still runs fine, with no CEL or anything. Still idles great (other than this morning). I'm going to top off the coolant and check everything else, but I wanted to hear some suggestions since I can't look at it until I'm off work.