So I recently had a good amount of work done to my car which I have had back for only a week now and now I am having more problems...

2002 A6 3.0L Quattro

(Coolant leak and overheating - AudiWorld Forums)

That is my previous post from about two weeks ago.

All of the sudden today my car started to rumble when it is idling. Along with that there is a bit of a sour smell coming out of the exhaust and what sounds like a very light ticking sound. Once I got up to about 30 mph the car would seem totally fine, but when I accelerate the vibration comes back and stays until I get to about 30 and start to coast, then it only comes back when I am stopped again.

From searching a bit on here my guess is that a vacuum hose came loose? Or could it be something more serious like a misfire? After spending close to 3k just a week ago I really don't want to have to spend another couple thousand to have my car running like it should be.

 

My 3.0 2002 a4 had a similar issue, below us what I tried. IMO the 3.0 is a flawed engine and should have been designed better from the start.

I had vibration at low revs and idle, no error codes at all. In the end it killed one of the cats.

Checked for vacuum leaks
Replaced coil packs
Changed Cambelt and re timed
Checked tensioners
Blanked egrs
Checked compressions
Cleaned injectors
Replaced plugs
Removed inlet manifold (absolutely ruined inside, the plastic intake tract length adjustment had gone brittle and cracked up into bits which left pieces of plastic on the backs of the valves!) replaced that.
The dual mass flywheel failed so had to fit a new clutch along with the flywheel

After all that it still vibrates and misses slightly.

Gave up and gave it to my brother in law as he needed a car to get about in. Still troubles me to this day.. Can only think it was a faulty/sticking valve but I'd lost patience and bought another car...

So in short check the intake for leaks as they're really sensitive to that or the overheating you gave it may have left a problem with a head gasket, get a compression check done. Don't throw too much more cash at it as I did if you can live with it, as you'll never get it back.