I am sure your problem is related to mixture control. Sounds like the mixture is changing for some reason and the idle control is attempting to hold the RPM constant until it is unable to do so and then it dies. The idle control valve will chatter when it reaches it mechanical limits of travel on the plunger. Maybe thats is what you are hearing. I would look for problems elsewhere, not in the idle control system.
Could be the Lambda system or the EHA or something in the fuel delivery system - pumps, filters etc.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k