Yeah, a lot of people say different things, I know. I feed my dogs a strict diet that does not include any filler type foods. I try to mimick the natural diet of a carnivore as much as possible. Some people are far more lenient with the raw diet than I am. Pasta and cooked chicken every now and then won't hurt him, but it won't provide all that much nutrition either. Maybe someone told you to give him that for his digestive problems? Simple foods like that are easier on the digestive system, but pasta and cooked chicken shouldn't make up his permanent diet. I don't see anything wrong with giving him that or a similar mixture on the rare occasions when his stomach is upset and you just want him to eat a little something. Or like you said, a couple of times per week probably won't hurt him. I would ommit the pasta, though. In those cases when you want to give him something simple, maybe you could try lightly browned chicken or beef cubes with diced carrots or something like that.
Lots of people are wary of the raw diet, but you should know that these are the types of foods wild dogs are physically engineered to eat. In the wild, they would eat bones, meat, organs, and all sorts of other things not found in kibble. Their jaws are strong enough to crush bones, and their digestive enzymes are much stronger than ours. That's why they can eat raw chicken and not be effected by the salmonella bacteria. Dogs are carnivores, and have biologically adapted to a diet that is nearly 100% animal products. I know dogs have lived normal lives on kibble for many years, but that doesn't mean kibble is the best diet for them. A person could live on cheerios for their entire life, but they'd be a lot healthier and fit on a balanced and biologically appropriate diet.
If you decide to go with the raw diet in the future, the best way to switch them is to just do it. They're digestive system recovers far quicker when they're switched completely, rather than weaned from kibble. Another thing that helps is to fast them for 12-20 hours first so they can fully rid themselves of any kibble still in their system.
I can't say for sure that he's getting motion sickness, but that's what it sounds like to me. They only get over motion sickness by riding in the car enough times to build a tolerance to the motion. Some dogs take longer than others, some get over it really fast. I would expect that the next time you take him will be better than the first, but again, some dogs take a long time to get used to the car. Just be sure not to feed him much (if anything) before he rides in the car, and keep him hydrated to reduce the effects of diarrhea (if he gets it again).