I have been willing to clean my intake valves for quite a while now. My car has 78,000 miles now and runs good but the idle was not very smooth and I had some slight hesitations on the highway at around 2k rpm, when using 40-50% of the gas pedal, but nothing major. I dont think the car had even go the valves cleaned in the past.
This is the DIY I used which is very comprehensive, thanks Rotorocious very much for it http://www.e90post.com/forums/showthread.php?t=520922
I used the B12 Carb Cleaner from Autozone (1 bottle for 2 cylinders) and some brushes from Walmart. It took me several hours as the valves have to soak for like 30min each + the scrubbing. You can clear the valves two by two usually.
It is a pretty easy thing to do if you have a garage at home, as you will need light and space.
The only problem I had was to remove the radiator fan to be able to rotate the crankshaft. That fan is attached at the bottom by a screw, that you can access only from under the car by removing the lower cover and then you can access the screw. But this wasn't mentioned in any DIY I found.
It is basically a job of unplugging stuff to access the valves and putting everything back together after.
I used a regular vacuum cleaner and made a filter out of an old t-shirt and connected a hose to the vacuum line to soak the dirty carb cleaner from the valves.
The only surprise I got was that I found a chicken wing bone sitting on top of the transmission, behind the engine. I don't know how it got there and how it stayed there...
Anyway, I also took the opportunity to paint my calipers in red.
In conclusion, it is not a hard job to do, if you are not afraid of disconnecting pipes, that's basically all it is to access the valves. Remember to mark all your sensors and pipes so you won't reconnect them in a wrong way. The total cost of the cleaning with all the tools and cleaners was under $40. Well worth it I think.
BBQ and beer for lunch with friends while the valves soak in the carb cleaner is highly recommended.