No reason to hold E, it'll work just as well if you just hit it.
Unless the problem is a "bad" gauge, as I have seen in
the past. Some panels that I have installed had gauges
that were interfereing with multiple key-stroke commands.
They would be sending continuos "KEY_" events every
simulation cycle. This causes a multi-KEY event like
E+1+2 to be broken up and the 1 and 2 are unrecognized
by the software.
The problem would only come to light once one tried
to take control of individual engines or inadvertantly
entered "E".
Paul