Stock 737-800 Autopilot

[Steamer]

Hi, brand new to the forums, but have flown FS2002, FS9, and now flying FSX.
Usually fly singles or twins, but now trying to fly the big iron...
In the 737-800 (stock) I have set up the flight planner, loaded the IFR flight plan, taxi out, and take off.
Crusing at FL300 300KIAS havin a big old time, and about 100 nautical miles from my destination, the nose starts porpising, (up and down oscillations), the aircraft starts losing altitude, and the autopilot, flight director, heading hold, airspeed hold, all are all still active.
So...

[garymbuska]

I could be in left field on this. But are you sure your anti ice is turned on.
if this was not a long flight you could be icing up and that will cause the speed to go crazy and all other kinds of problems.  I have not had this problem and being you are new to jets you could easly over look the anti ice and pitot heat. 8-)

[Steamer]

Thanks!  I will try that tonight, when I get home from work...