306 D Turbo rough starting

[Steve_D]

On startup I'm getting misfiring and smoke which all clears up after less than a minute.
I'm suspecting the glow plugs.

Is there any way to test them? I tried a temp gun on them with inconclusive results.

Are they known to fail and should I just regard them as a consumable to be changed like spark plugs?

Any make to avoid?

A cheap source?

Any other reason for the problem?

Thanks in advance
Steve