On ignition there is a large (sometimes) burst of white exhaust but not always and only after the car has been idle for say 4 or 5 days. What is the problem and is it worth repairing or is it time for a new car?
White Exhaust smoke on starting after the car has been idle for several days on 2003 Saab 9-5
It is possible that the head gasket is starting to go bad. Have you noticed if your coolant level is low or looks murky? In my opinion, even if it needs a head gasket replacement it is still worth fixing. A properly maintained Saab can last a long time. I have seen 9-5s with well over 200,000 miles still doing well. I have even seen one with 395,000 miles.
There's also a fair chance it's the Turbo. I'm more familiar with Turbo issues on the 9-3, so that may not be a "common" issue on an '03 9-5, but something to consider as a puff of white smoke on start up is traditionally indicative of turbo seals going out.
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Check your turbo!!! The white is most likely anti-freeze that's getting into the cylinders...that usually indicates 1) head gasket/cracked head or 2)Turbo problems (if so equipped). I have experienced both...Yay!