Possible MAF problem on 99 Grand Prix ?

My 1999 grand prix died on me last week while driving. I tried starting it a few times, it would start and unless i kept the RPM's up it would die. Even with the RPM's up it ran very rough and rich ( you could smell a heavy gas smell ). I had it towed to the repair shop for it only to start right up.
They couldnt find the problem as it showed no codes.
I drove it away and it ran fine for about 20 miles then died again. I had it towed home this time. Some times it starts and runs fine, other times it start but wont hold an idle and dies.
When it starts, again it will start but not hold an idle without keeping the RPMs up, and it runs very rich.
I had the crankshaft sensor replaced abourt a month ago, so i doubt its that .

Any help would be appreciated.