When my air hose was disconnected from my intake pipe (See my reply to TomEboi's last thread on this topic), I was getting the same erratic idle that everyone is describing but there was no check engine light.
Check around the MAF for leaks. If you can't find the problem yourself if a few minutes, then you need to find another dealer. These problems should not be hard for good professional mechanics to solve.
The only other thing I could think of is that maybe the sensor on the MAF is self could be damaged.
------------------
2000 GT --
Black, 5sp, Mach460, Bassani CatBack & X-Pipe, MAC Cold Air, 70mm Tbody, Hurst Shifter
1966 Mustang Coupe --
Tahoe Turquoise, Pony Int, A-Code, C4 Auto
------------------
scott@pearland.com