Serious backfire, shaking idle, engine goes out??
 

Guys Help me!

My Audi a4 Avant 03' 2.0 ALT suddenly from one day won’t idle correct. When warm the idle is very rough and there will be a lot of backfiring in the intake manifold (I think) but it will remain going. When cold the story is the same but it will go a little bit lower in RPM and eventually go out. I checked the VCDS and it said “misfire detected” on cylinder 1 and 4, so I changed the coils and plugs on all 4 cylinders. There was no difference!
Then I tried measure the MAF reading on full throttle with VCDS. 102 g/s. with a 130 hp car it should be 104 g/s, so I assume MAF is ok ?
Then I tried pulling the throttle body of, looked fine inside, cleaned it a re-fitted it.
Then I checked the wiring at the coils, also fine.
So now I looked a bit through this forum and found an old topic about a V8 who describe an issue a bit like mine, and someone told him it could be the cam chain tensioner. Funny cause I had that in mind also. Therefore, I pulled the valve cover off and looked at the cam and tensioner, but what to look for? The pads looked fine and the chain was tight. But was if the timing isn’t correct between the valves? How can I check that?
If I understand the system correct the little solenoid on the back of the cylinder head adjust the timing between the cams by slacking and tighten the cam top and bottom? If that’s so, then the chain can be thight, but the timing can be off?? How can I checked if that’s working? Can the VCDS help me ?

The car has 290.000 km on it. And it uses a bit of oil. It also have had the clacking when starting it, like a bad lifter. My plan was to do a piston ring change soon, but not if I cant find this mistake first.
So please help me, all feedback are welcome
Thanks