Mxsmanic wrote in
:

Within what limits? I fly to a heading and then 30 seconds later when
I check it again I've drifted two degrees or so and have to move it
back. Altitude is a much bigger problem, with a constant
roller-coaster ride through as much as 150 feet or so for quite a
while. By the time I wrestle it onto a steady altitude, I'm being
told to climb or descend again.

The accepted limits are documented in the Airmen Practical Test Standards,
which you can read online he

http://www.faa.gov/education_researc...ards/pilot/med
ia/FAA-S-8081-14A.pdf

The limits for Instrument flight are slightly "tighter" and are documented
he

http://www.faa.gov/education_researc...ards/media/FAA
-S-8081-4D.pdf

2 degrees of heading is acceptable. 150 feet of altitude, however, is not.