@martinhoos,
Try below modified iLogic code with respect to previously attached iFeature file(.ide).
Public Sub Main()
Dim oPartDoc As PartDocument
oPartDoc = ThisApplication.ActiveDocument
Dim oPartDef As PartComponentDefinition
oPartDef = oPartDoc.ComponentDefinition
Dim oWorkPoint As WorkPoint
oWorkPoint = ThisApplication.CommandManager.Pick(SelectionFilterEnum.kWorkPointFilter, "Select a point to place iFeature")
' Get the selected face to use as input for the iFeature.
Dim oFacePlane As WorkPlane
oFacePlane = ThisApplication.CommandManager.Pick(SelectionFilterEnum.kWorkPlaneFilter, "Select a Plane to place iFeature")
Dim oFeatures As PartFeatures
oFeatures = oPartDef.Features
' Create an iFeatureDefinition object.
Dim oiFeatureDef As iFeatureDefinition
oiFeatureDef = oFeatures.iFeatures.CreateiFeatureDefinition("Path of ide file")
' Set the input.
Dim oInput As iFeatureInput
For Each oInput In oiFeatureDef.iFeatureInputs
Dim oParamInput As iFeatureParameterInput
Select Case oInput.Name
Case "durchmesser"
Dim oTubeDia As iFeatureParameterInput
oTubeDia = oInput
oTubeDia.Expression = "16 mm"
Case "Ebene1"
Dim oPlaneInput As iFeatureWorkPlaneInput
oPlaneInput = oInput
oPlaneInput.PlaneInput = oFacePlane
Case "Punkt1"
Dim oRefPoint As iFeatureEntityInput
oRefPoint = oInput
oRefPoint.Entity = oWorkPoint
End Select
Next
' Create the iFeature.
Dim oiFeature As iFeature
oiFeature = oFeatures.iFeatures.Add(oiFeatureDef)
End Sub
Meanwhile, iFeature is failed to add into part document through UI as well. I think, model is failed to regenerate after updating parameter(durchmesser). On parameter update, below error is thrown.

Thanks and regards,
CHANDRA SHEKAR G
Developer Advocate
Autodesk Developer Network