Opportunity to purchase a 1 owner 240 GL w/112k miles off of a dealer who knows nothing about Volvos. Car starts, runs and drives well. Idle I think is a bit high, around 1050. Car will not pass echeck/emissions. Says its is running to rich. Exhaust tail pipe is really deep black and sooty. Car has had air mass meter replaced, oxygen sensor and exhaust from converter back. Dealer replaced spark plugs hoping this would help, but hasn't. Any thoughts? Car is priced really low, but don't want to get into a grand or more trying to pass emissions. Thanks for everyones input.