Volvo C30 2.0d cold start problem

[FictiveS]

Hey guys,
I'm having a problem with cold starts if the temperature is below 10 C. The car cranks longer, and if colder, like 2-5 C, it cranks a long time. Once it starts I get a cloud of smoke that smells like unburned diesel. The car sounds rough and smokes for 2-3 seconds tops. When I floor it, it does not produce any smoke.
Afterward, it is very smooth, and during the day I have no problems starting it again. Only when it sits overnight.
I tried leaving it in the garage as it is warmer, and in the morning it starts without any smoke or problems.
There are no codes at all.
My question is, is it possible that glow plugs are bad and it just doesn't throw any codes? I read about the possibility of glow plug relay problems, but everyone seems to think that it would always throw a code.
My mechanic thinks maybe there is a problem with the engine, as it is not throwing any codes, but it sounds unlikely as I did not have any problems during the summer and once it is warm, it pulls and runs smoothly. Or maybe he is using a generic code reader, as I did not ask.
Should I just go ahead and change the glow plugs and maybe the relay as well?
Thanks!

[Simmy]

test the glow plugs insitu. replace any faulty ones . dose your glow plug indicator light on the instrument panel light if so turn ignition on till glow plug light goes out then try starting .

[FictiveS]

Originally Posted by Simmy

test the glow plugs insitu. replace any faulty ones . dose your glow plug indicator light on the instrument panel light if so turn ignition on till glow plug light goes out then try starting .

It does, but what is strange is that it only flashes. It is basically on as long as other control lights are. Maybe 5 seconds regardless of how cold it is. It was -2 C the other day, and it stays on the same amount of time as in the summer.
Would you suspect anything else besides the glow plugs?

[Simmy]

flashing glow plug light may be its an indication of failed plugs. test them with a multi meter. there are youtube vids explaining how to do this. if all check out ok test the relay or replace if found faulty. do a leakback test on the injectors .there is an injector testyou can do with vida if you have it .other more expensive testers can also do this type of test.

[FictiveS]

Would a leaky injector cause cold start problems regardless of the outside temperature? As soon as the temperature drops to like 10 or lower it starts happening. But everything above that, it would start fine.