help 99 s70 awd with 100k coming back from NY to Detroit in 95 deg. temp started to run ruff. surging & milage dropped to 14 mph. running real rich with black smoke & all. at idle almost wants to die. made it home thank GOD. went to auto zone & pulled codes p1171 manufact fuel air metering & p0171 system to lean. called local guy & he stated start with the mass air sensor. rest computer prior to getting new part & ran fine for under 1 hour . anything over 1 hr. getting the bucking again. rest again. finaly new mass air sensor installed .wife had to drive 250 miles in 93 temp ,same bucking again. took new sensor back & installed old one & rest comp. again. talked to a few volvo service dudes & the said poss. the throttle controll mod. help where is it? whats it look like? & any other suggestions would be helpfull . thanks brad