First of all, which model it is? Here is a link to the S/V70 model specifications for the '98-'00 when these first platform 70 series (P1) were made:
http://forums.swedespeed.com/zerothread?id=7170
Similar issues as 850's over-all, but not as bad of an A/C evaporator...but if it goes bad, still $1200+ to repair. Other than this, the '98 is prone to have a bad ABS module, but a guy here fixes these for cheap. PCV systems need cleaning to assure you'll keep your rear main seal, but it's not expensive..just a pain in the rear to do. Pretty much solid cars...highly recommend the '98 over the other two years. It's the only one with a non-electronic throttle module (ETM) which have been terrible to mess up on the later models. Though covered under an extended Volvo warranty, it could go without warning and they you could be stranded, so once again, look at the '98 models. I personally have a T5 and love the high pressure turbo and extra power. Also a lot of mods out there for these cars, but don't expect to get a lot of boost or for there to be a lot of mods for the non-turbo model.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.