1.
If you fiddle around or fiddle about with a machine, you do things to it to try and make it work.
Two of them got out to fiddle around with the engine.
= tinker
PHRASAL VERB : V P with n , also V P
2.
If you say that someone is fiddling around with or fiddling about with something, you mean that they are changing it in a way that you disapprove of.
Right now in Congress, they’re fiddling around with the budget and so on...
PHRASAL VERB : V P P n [ disapproval ]