Unexpected *-dh-

Stang (Slav.-Balt.-Germ. lexikaische Übereinstimmungen) compares
veldéti/vlasti/waldan with Lat. vale:re, adding: "Ich bin daher
geneigt, ein balt.-slav.-germ. Präsens mit dh-rweiterung aufzustellen".
Elsewhere he doesn't know how to account for the -d- in Slavic id- "go".

I was wondering if the *-dh- was due to a back-formation from an
imperative in *-dhi? So, (Russian) idú from idí?


Torsten