I thought if you gave godlike power to someone who already had super-speed, they'd get more done.

Well, he still manages to do a ton of damage: from 2002, Impulse #87, "Crisis on Impulse's Earth, part two" Written by Todd Dezago, pencils by Carlo Barberi, inks by Greg Adams.

The Phantom Stranger seemingly implores the reader to "observe your boy" as this one opens: using a newfound time-travel power, Impulse had stopped the mystical entity Bedlam by taking those powers himself. (As opposed to letting a more troublesome host, Matthew Stuart, take them.) With near-infinite power, and absolutely no foresight, Impulse starts with fairly innocent changes like bringing back his dad and aunt and grandpa--the Tornado Twins from the 30th century, and Barry Allen! Then he gets down to the business of making the world a better place: fixing the hole in the ozone, making cars fly and run on water, giving dogs the power of speech; and a few selfish ones like outlawing asparagus and making the school week two days.

Bart's friend Carol points out that Bart's changes are all having unintended consequences: even saving the whales has messed up the food chain. Worse, the Twins and Flash point out, they died heroic, necessary deaths: if Bart took them out of the timeline, was that going to cause problems? Luckily, the Phantom Stranger hadn't been talking to the reader about fixing this, he was talking to Max Mercury! Who helps convince Bart to give up the power, then disappears since with the magic removed retroactively, Bart didn't save Max from the Rival. Still, Bart does think ahead at least a little: writing a note to himself on his hand, he uses one of his time-travel "scouts" to plant Carol's notebook on the Stranger, so he can retrieve it after his magic and his memories of it are gone. The Stranger doesn't seem to notice, but Bart seems to have something in mind...is the idea of Impulse with a plan terrifying anyone else?

The Phantom Stranger of course may have since gotten into "hop hip," we've seen him drop some rhymes. The medallion should've been your first clue...There were only a couple issues of this series left, and I think it may have ended with Max still possessed by Rival or something; a leftover from some crossover. Without looking I'm honestly not certain if Max Mercury has returned in the New 52, since a mentor figure like him would be seen as taking away from "Saint Barry," but then again I know there's like 90 speedsters out there, too...