The car suffers from an annoying condensation problem in the distributor cap. If it's left in the rain for a few days without running, it sometimes gets water condensing inside the distributor after about 20 mins or so of driving. This leads to misfiring and eventually stalls the engine. The only cure is either leaving it to dry naturally for about an hour or taking off the cap and drying it by hand. This is a real pain when I've got to get somewhere on time!
It's also got a stalling problem which appears every few months and doesn't seem to be related to anything in particular. I think it's a problem with the idle cut off solenoid valve or maybe something floating around inside the idle jet channel in the carb. It's not too serious since I can always pull out the manual choke to keep it running.
I've spent a lot of time treating some rust problems. Both wings have been off and some reconstructive welding has been done to the outer wheel arches. There is no serious structural rust - yet.
There have been a few minor problems such as a seized central locking servo and a ruptured coolant hose.
Let's face it, the 340 is not a sports car but I'm quite attached to it. It has an acceptable performance with a 1.7 if you make full use of the accelerator pedal :), just give yourself plenty of room for overtaking. One thing to watch out for is the tail end sliding away as you round a corner.
Motorway performance is adequate with a 100+mph possible although I don't recommend full throttle for extended periods of time. Fifth gear keeps the engine noise down but it's a bit sluggish going up inclines. It's quite comfortable at 75-85mph except for excessive wind noise from the door seals.
It drinks petrol. I can squeeze about 30mpg with gentle driving but I tend to drive it as fast as it'll go so 25mpg is more typical. The fuel tank is on the small side and only gives a range of about 220 miles.
If you like working on your car then you'll find that there is a fair amount of room in the engine bay. Most things can be reached easily, especially the spark plugs.
If you go to a Volvo dealer for servicing, be prepared to fork out a large wad of cash. Better to find yourself a good local mechanic.