In SERIOUS need of guidance/advice...

I have a 1988 760 turbo intercooler wagon. The turbo's been guzzling (or something?) oil for probably as long as I've had the car. The car has driven 155K miles. I have 5 more payments @$166.16 each before the car is truly mine. I've had a costly 2 years and 7 months with this car and am afraid that it's time to say good-bye. Currently, it's choking out big clouds of black smoke and struggling to get to 40mph, after which point the sluggishness isn't as bad. The body/interior of the car look great. Main drawback besides the turbo issue is the busted A/C. Otherwise, little things like---no more cruise control, power sunroof and 2 power windows are dead, gas gauge dead, power seats are questionable.

MY QUERY: Should I try to keep this car? If not, sould I let it go 'as-is' or have the turbo replaced/rebuilt (which?)I forgot to mention that the rear wheel on the passenger-side has, on two occasions, been dangerously close to coming off---two of four lugs gone, others comletely loose. The only explanation I've gotten for that has been question of the likelihood that I may have an ENEMY. Neither my iffy-at-best mechanic,nor the folks who put new tires on the car a year ago can give me any insight, just the enemy response. I'm in desperate need of help. I know that I cannot continue to drive the car in this condition (unless I want to replace the exhaust system...), but I want to explore options with people that I probably trust more than those who've worked on the car. A good Volvo mechanic is scarce at best in Rome, Georgia. I bought this car for $5K with 110k miles and have had a list of problems making me feel like I got a bad machine (repairs have equalled roughly $1800). I had an old '84 240 that I absolutely adored, but this one could very possibly have jaded me to the point of no return. I'm open to any and all suggestions, advice, etc. that may help me make a decision soon, soon, soon. THANK YOU!