What is the difference between приду and прийду?
Both mean: I will come?(on foot)
Also я приеду and я прийеду mean: I will come?(by vehicle)
Again what is the difference of them?
Прийду is an outdated norm, the verb идти and its derivatives being, probably, the most miraculous of the Russian verb family representatives.
E.g., there were three ways you could write прийти, which were придти, притти и прийти.
Leave alone the fact that the verb идти is an infinitive ending in ти instead of ть, like all the other infinitives.
It seems to be just logical, that the infinitive прийти should make up the personal forms я прийду, ты прийдёшь, etc., and it was actually a norm. And it sounds like that. But nowadays the й has remained only in the verbs not containing и like подойти, отойти, уйти: я уйду, ты уйдёшь.
The ий has been assimilated and reduced to и. Nowadays it's just one и there. Приду is the norm.
And прийеду is not more than a mockery based on the analogy with the verb прийду. )))))
"Прийду" and "прийеду" are ungrammatical. While "прийду" is a common mistake, "прийеду" is simply totally off.