I do a lot of short journeys now so sooting up of the EGR is a regular feature. I have one of the restrictor plates with a 10 mil hole - which supposedly slows down the clogging but it certainly doesn't stop it. The plate doesn't cause a check light and I have been cleaning the valve every few months before the computer picks up a problem.
I had been using the carb cleaner and tooth brush method and could get it fairly clear but not perfect. So last time I tried something more drastic. Oven cleaner.
Now I know oven cleaner will eat through alloy, etc, etc and people will say don't try it. But the fact is that the stuff I used - Xanto Power Activ - dissolves the carbon in seconds and can be hosed out long before it starts to work on the metal. The result is amazing. The valve looks almost new with minimal effort. And since I used this method, the car - with 106,000 miles on the clock - drives better than ever. No lumpiness at low revs and really smooth acceleration. Also much improved mpg.
I reckon I used about 20p worth of the cleaner and because it works so quickly, it was a genuine half hour job, allowing for a minute or two with a heat gun to dry it out before refitting. I did squirt a bit of carb cleaner onto the diaphragm and wiped round with the spring depressed to make sure the mating surfaces were clean. (Not a good idea to poke your fingers in there with the oven cleaner...)
Obviously, you try this at your own risk but I was surprised how quickly and effectively it worked. Provided you slosh plenty of water in there as soon as the carbon comes out, no harm seems likely to the metal or engine. Well mine has not suffered in the slightest. Gloves are recommended to avoid burning skin.