I'VE GOT AN 98 S70 THAT STALLS WHEN I'M AT A STOP SIGN AND IN THE YARD IDLEING THE RPMS GET BELOW 1000 AND BLACK SMOKE STARTS BOILING OUT THE MUFFLER BUT I CAN PUT MY FOOT ON THE BRAKE AND MASH THE GAS AND IT WILL CLEAR UP SOMETIMES I HAVE REPLACED THE FUEL FILTER THE PLUGS AND WIRES AND I HAVE TAKEN IT TO A FRIEND THAT HAS AN COMPUTER TO CHECK THE CHECK ENGINE LIGHT AND THE CODES SAY MASS AIR FLOW SENSER AND #1 FUEL INJ IS TO LEAN PLEASE HELP!!!!!!!!!!!!!!!!!!!!!!!!

 

Check for vacume leak right by throtel body common leak on flame trap. If that is not it, then check into replacing the air idle control valve.

 

I had the same problem with mine. It was the MAF.