George - I carried out a detailed investigation a while ago - see "Spanish '-ir' verbs"  at http://dlmcn.com/ir_verbs.html - and can confirm that all '-eguir' verbs do indeed follow that same pattern - as too do all verbs ending in '-etir', '-egir', '-edir', and '-eir' [plus a few others].

On the other hand, all '-ertir', '-erir' and '-entir' verbs change the "e" to "ie" when conjugating their present tense...

... while three '-ergir' verbs retain the "e", making no vowel-change in the stem.

Thanks