PA380 Lose Altitude when LOC Captured.

[jason2000915]

When establish LOC I have no control about plane's altitude unless I fly it manually.Otherwise it keep losing altitude very fast.Ive tried using the v/s but no result.Also if I use the HDG mode to turn the Airplane at a low alt like 3000FT, It loses alt as well. I experienced this too when I fly Wilco Airbus Series.If somebody know the solution please tell me.thank you!

p.s:My aircraft is not overweight.I double checked that.And im using fsx version merged VasFMC 2.1