I would think, as SCM does, that he is hungry and his belly is a bit upset. I would leave some canned food out for him to munch on overnight.
I bet if you did a gradual increase of canned/gradual decrease of dry that Gizmo's diarrhea issues would get better. It is normal for a cat to have diarrhea with a sudden diet change but, with time, it improves. It is the same as us if we eat something we normally don't. Like more veggies in your diet.
You could try maybe a tblsp of canned to start gradually, over the course of a week or two, increasing it till he is eating almost all canned and very little dry. It really is healthier for him to be eating canned.
If you don't want to do that would you consider dropping the Iams and trying a corn free, grain free dry. Corn is not digestable for us. I don't know why the pet food industry insists that cats and dogs can digest it. In fact they can't. Grains are also not a good choice for an obligate carnivoure such as cats are. There are some good options available at Global or Pet Valu pet stores.
A really good web site to read is www.catinfo.org
. Some of the info in there is mind blowing.
Oops, I think I read that wrong. Is it the Iams they get three times a week or the wet?