I just did a MAF to SD swap and it ran beautiful for the last few months. All the sudden yesterday it started idling badly and died on me at a light. Now it barely runs very choppy and intermittently accelerates. Today on the way home it just sat there sputtering and not responding to the throttle at all. When I popped the hood I noticed that it seemed to be sucking in way too much air just idling. It's puffing grey and black smoke too. Help!

 

Assuming it's not EFI related, an intake gasket leak would fit what you described.
Check your plugs. If they have what looks like baked grease on them...