Re: running rough
Glow plugs only warm the incoming air charge when the temperature is below freezing, or close to it. Diesel fuel waxes at colder temperatures which slows the flow of fuel. Diesel fuel pumps are relatively a lot slower than comparable gasoline units which aids in startability as a pump that pushes a lot of fuel (in cold weather it would have to pump a lot of gelled/waxed diesel that can wear out the motor).
I'd do some maintenance checks first, such as fuel filter, and replace the water separator. If the water separator is full of water, some will enter the fuel system causing starting problems as the engine isn't hot enough for the water to evaporate. Watered down fuel will cause problems, even if it's not much. Make sure the air intake is also clean. Filter minders don't always work, so be sure to check the filter at least once a month unless you drive it 100miles a day, then check it weekly.
If the weather is cold, I suggest plugging in the block heater to aid in starting. This will make the glow plugs more efficient and they won't have to run as long.
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!