Has anyone experienced this code?

when it happens, it dose only at the end of a run ad the idling goes up and down slightly to indicate the DMA is compensating for a leak.
I verified all the turbo ducts and all are o.k. .
The only items I haven't checked is the throttle body and the vacuum hoses
underneath the intake manifold. May be one of those is the culprit of a leak?

Anyone has some input?
The Bentley manual says the code signifies : '' DOWNSTREAM THROTTLE AIR LEAK''

COULD IT BE THE MANIFOLD GASKETS?

Thanks