BE35 pilot reported engine failure after selecting the right fuel tank with the cross-feed valve. The pilot immediately selected the left tank; restarted the engine; and returned to departure airport.

Narrative

I was in initial climb on IFR flight plan from ZZZ to ZZZ1 when; at stated position; I switched fuel tanks from the left tank to the right tank and lost engine power immediately. I executed memorized emergency procedures to switch fuel tanks and activated boost fuel pump; and I simultaneously [requested priority handling] to ATC [TRACON] ZZZ; then located ZZZ2 off my left. [I] began a slight descending turn in the direction of ZZZ2 at published glide all within a second or so of losing the engine power.ATC was very helpful - if I recall correctly; they offered me ZZZ2; and then as I got the engine running again in just a few seconds; ATC then offered me a return to ZZZ which I took and accepted given my altitude. I landed at ZZZ; base; without incident.Upon further review; I determined that the engine outage was caused by residual air in the fuel lines from a maintenance visit the prior week when our tanks were drained to determine proper weight and balance. After that maintenance; I performed a ground run-up test of both tanks. I followed that with a high-speed taxi test of the left tank; but not the right tank. It is entirely possible that the lower-power run-up on the right tank was not sufficient to pull all the air from that line.The takeaway is that after any fuel maintenance; it is critical to do a ground test of BOTH tanks; to full power. I will also perform a high-speed taxi of both tanks to ensure I achieve full-power and remove any residual and expected air in the fuel line(s) as part of our normal post-maintenance test procedure.This was an excellent demonstration of the ATC system responding in support of a real emergency. No issues here from a regulation perspective as I see it; but I did want to file this for the sake of learning" on the importance of post-maintenance testing that goes beyond the obvious; basic run-up. This could have avoided this situation for all. Thank you."