What is my food intolerance?  Is there a way to test for it?
After eating at a restaurant, I typically have diahrrea within 1 hour,
sometimes within 24 hours though.  This occurs only when I eat at
certain restaurants.  I usually eat chicken sandwiches and french
fries, pizza, and things like that, no sea food, or other unusual
foods.

Diahrea episodes:
Unos - Grilled Chicken sandwich with lettuce, tomato, and some sauce,
fries, and slice of pizza.
Country Tavern - Chicken Boursin (chicken, broccoli, cheese, baked
potato, veggies, salad)
Many Pizza restaurants - plain cheese pizza 

Know safe food at these restaurants:
Wendys - Chicken fillet sandwich, fries
McDonalds - chicken nuggets, fries
Burger King - chicken fillet,  fries
Chineese Food - chicken fingers, rice, beef teriaki
Subway - Chicken sandwich * (usually no problem)
Foodees Pizza 

I don't have this problem when I eat food that I make at home.
Foods that are safe for me are:
pasta el forno (pasta, home made sauce consisting of crushed tomatoes,
garlic, shallots, onions, heavy cream, parmeseanio reggianio cheese)
stir fry (veggies, rice, chicken)
Baked Potatoes, corn, veggies, cheese
olive oil, grape seed oil
home made cookies
package mix of brownies
ice cream 
chips, snacks, etc.
salad
french dressing
italian dressing
rice
cumin, garlic

I've been tested for lactose intolerance and that test was normal.  I
can avoid the problem by not going out to eat ever again, but I would
really like to know what kind of food to avoid.  I suspect my
intolerance is an oil, spice, or flavor enhancer, or something like
that because I can eat the same food if I make it myself.  Doctors
think I have irritable bowel, but I know that something triggers it,
and I want to find out what that is.

Trying an elimination diet is not going to work for me because I don't
have this problem when I eat at home, and I don't know what
ingredients are hidden in restaurant food.

Okay, for starters you have to change your diet. You'll be on statins
soon and getting angioplasty not long after, based on what you eat.

No matter what I eat at a popular chain restaurant (it rhymes with
Shmolive Shmarden) or which one I go to, it always makes me ill. I
finally put it down to system-wide questionable handling techniques
(note to Shmolive Shmarden attornies-- I didn't say it was
questionable food handling techniques, questionable flatware handling
techniques, questionable hygeine handling techniques, or even
questionable question handling techniques, so you've got no case) and
just don't go there.

Somehow I soldier on despite the crippling limitation this puts on my
life. You can, too.

It's no answer, but you get what you pay for. Best wishes!

Olive oil? Basil? You suspect oils and spices. Buy a variety of them
and try adding them to your meals.
Celiac disease, which is an allergy to the gluten in grains causes nasty diarrhea.

I guess from reading that, you think I eat chicken and fries all the
time, but really I eat out at fast food once a week.  I have normal
blood pressure.  At home, the food is whole wheat pasta,  whole grain
rice, whole wheat bread.  I do eat a lot of chicken though, almost no
red meat.   Most things are made from scratch because I have to skip
the sodium in most recipes due to other family requirements, except
for when I eat out once a week.  I do try to have vegetables or salad
as part of every dinner, but I could improve with eating more fruits
and veggies.  It's those starches that I eat too much of.

Please see the webpages for more details on food intolerance and food allergy. 
http://www.nlm.nih.gov/medlineplus/ency/article/000817.htm
http://en.wikipedia.org/wiki/Food_intolerance