I am not sure why, but when I fly the PMDG 747 and increase my acceleration rate, the auto-pilot can't maintain the set altitude. Does this happen to anyone else and can it be remedied?Thanks.

How much are you accelerating time? I've noticed some dips in rough weather at 4X, and I imagine any faster would make it very pronounced. I'm talking maybe +/- 50 feet. If the oscillation is accelerated I imagine that would increase by a lot. When I do speed things up once in a while, I never run faster than 4X due to AI disappearing. Basically I think it boils down to accel. rate and how sensitive/powerful the autopilot is.

In the first "chapter" of the most excellent manual (PMDG 747‐400X ‐ AOM, Revision – 26SEP07) which comes with the 747-400 for FSX, there is a section on page 0-39 called "Time Acceleration Limit."The answer is there. The "Cliff's Notes" version: You can't use too high of a time-acceleration value or the autopilot won't function properly. Your manual will instruct you on what that limitation is.