Hi,

good, I had the feeling that it's the flap control. But if you really have an error regarding the valve, you should also double-check that one. I could imagine that somebody had a lecking valve once in the past and instead of replacing it properly it had simply been removed. Upside: cheap. Downside: It takes longer until the engine becomes warm.

Have a look behind the block and check if the valve is still there and connected (and if it's working).

Bastian

Das Buch zum Audi V8