My Rottie is BIG, most people tend to guess that he weighs around 150 lbs. In reality, he weighs 105 lbs. My parent's golden retriever is bigger than him, and in reality he only weighs 70 lbs. I had a St. Bernard that weighed 160 lbs, and looking back, she didn't look any bigger than my Rottie.
It's not about how big your dog is, it's about the problems you're having now. IF your dog is that big, and it's not a visual estimate, it's an actual reading on a scale, then you need to recognize that something is definitely not right with the dog, and you can't consider him "purebred" as far as what the breed standard defines. No insult to you, but I've found that many people overestimate their dog's weight just to make themselves feel better. "I have an 80 lb Rottie" doesn't sound as good as "I have a 190 lb Rottie" does it? Personally, my Rottie is a big tough, wussy, he looks like Arnold Schwartenager, he's built, but ideal for dogs from Germany is 120 lbs, he's short of that weight, but I love him anyway.
Even at his weight, we have a crate for him. We have 5 dogs in this house, and all I have to do is say "anybody want dinner?" and each of those 5 dogs go to their own crate. If we have friends over and it gets to be a little much for him, guess where we'll find him? He goes to his crate. He doesn't feel that the "cage" is punishment, if he did, he'd avoid it. He does seem to feel that it is HIS space, and we make a point of never reaching into his crate, or any of the Min Pin's crates. It's their space, if they're stressed, they go there on their own.
As far as feeding guidelines by Iams, have you looked into feeding a decent food? Thor gets 2 cups a day of Canidae. One cup in the morning, one in the evening, and he's happy. Last time I looked at an Iams bag, I think he should be getting a little over 5 cups a day. Also, he was extremely hyperactive when we fed him 4 cups a day of Eukanuba, and it turned out he couldn't deal with the corn in it.
If my wife wants one of her horses to turn a really good time on barrels, she feeds them straight cracked corn. It's pure energy to them, but she won't feed it on a regular basis. We won't feed our dogs anything containing corn, at any time, regardless of the reason. People will argue whether or not corn is good for dogs, but foods such as Iams, that are based on corn, aren't really addressing the needs of a carnivore, or even an omnivore, but if that corn affects dogs like it does horses, then it's no wonder a dog bounces off the walls.