The last time i seen this was on the Opel with the same engine .
We had a leak on the throttle body gasket was sucking in air .
Remove the throttle body and replace the gasket ring .or spray carb cleaner around the throttle body with the engine running at idle
you notice any change in engine speed then this is where the leak is .
MAF sensor is also been known to trip this code .
Have another smoke leak test and be sure manifold intake gasket etc.