I have an Audi Allroad. 2001. 152,000 miles.
It's been running great. When I first got it 2 years ago, I've replaced the plugs, coil packs, and both ICMs.

The other day I ran an errand for work.
On the way back, the car started misfiring.
I thought to myslef "the damned ICMs again??'
But, I had it scanned...twice, and both times it came up as p0300, multi random misfires. In the past, with a bad ICM, it just ran BAD, plus showed which cylinder was misfiring.
1)no specific cylinders.
2)Secondly, on the next day, I've noticed that it's trying to run normally.
3)It runs rough at idle.
4)When you put it in gear, whole car shakes.
5)When going down the road, you can hear it misfiring and then for split seconds it runs fine, then goes back to misfiring.
6)Under heavy load, the CEL blinks.
Some times it seems like it's going to run fine, has pick-up for a second or two, then back to shuddering.

What I have done:
I've cleaned and then disconnected MAF
Added gas and engine cleaner.
Looked over hoses, can't find any vacuum leaks visually.
Swapped out an old ICM with the two current ICMs with no discernible differences.
Checked battery connections, reset CELs.

Ever since I've had the car, I've had a CEL for one of the O2 sensors. I had taken it to Audi, and apparently it's common as the car ages, these O2 sensors are too close to the stream, and give a code) Never had any issues, and I've gotten an average of 22mpg.

Now, because it came on so suddenly, and on the highway, I'm thinking maybe the fuel system?
Fuel filter?
Fuel Pump?
Relay?
Fuel pressure regulator?

I am going to go buy a fuel pressure test guage to see if the pressure is correct and steady.

I have a Vag-Com cable on order, and hopefully this will help, too.

 

check and see if you vent hose is cracked or slpit along with your check valve