diagnostic code P0401

Actually, it is often more than the valve that needs cleaning. The first source has a good write-up on a different Honda engine, enough to give you something to go on. As the original contributor notes the valve is not necessarily the critical blockage. If you do remove the valve be aware that it may not be as simple as it looks. My experience was that a socket would not get to it (although it looked like there was plenty of clearance) and there was no room to swing a wrench. I had to use a crow's foot wrench to get it off, and both nuts were so tight I was in serious danger of rounding the nuts.

The cleaning cost, if you can prevent the mechanic from simply replacing the valve and calling it good, is about 1 to 2 hours labor depending on the engine design.

$4.99 if you do it yourself. All you need are a pair of needle nose pliers, a ratchet, a 12mm socket, and about 15 minutes. It's located right under the throttle body, and is held on by 2 12mm bolts, and has 2 vacuum lines attached. Once its off take the $4.99 and go buy a can of brake parts cleaner, spray the heck out of the inside. You will see a little rod, and a piston looking device. You will also see a LOT of carbon build up and the brake cleaner will dissolve it and you take a little wire brush and clean the inside after spraying.