I had the valve taken out for a clean today.
Remove the huge black cover of the air-cleaner (filter), and you'd see the valve sitting just infront of the fuel distributor. You might have to take off 2 screws holding it, and then gently nudge it out.
It looks like an artificial heart with the aorta.
Take that out and spray WD40 or equivalent into both the openings. Spray liberally to dislodge any dirt in it. It should be quite clean. The object is to ensure the pistons inside this valve (it really does function like a heart after all) is clean and allows it to function efficiently.
Then, having yourself satisfied its clean, give it a "blow job" to make sure its not dripping with WD40 (not too much though I did say liberal). Rreassemble. Start and examine your idle.
It should work.
Otherwise ... perhaps change the valve ... approx. USD100-00.
126 tailed by a 203, 129 leading the pack.