He said a new person taking over may want to "re-invent the wheel" and cost the party.
"It won't be a wise move to change him now ...we don't want to go backwards. I am not saying James is perfect‚" said Mngcwango.
He said Selfe was the right person to take the DA to the 2019 elections.
Mngcwango said is support for Selfe should not be seen as a campaign against any party member‚ including Steenhuisen.
"I am not talking for KZN [but] I will mobilise KZN delegates and I will mobilise delegates across the country to vote for James‚" he added.
Party leader‚ Mmusi Maimane is not expected to be contested at the upcoming conference but party chairperson Athol Trollip faces a stiff challenge.
Tshwane mayor Solly Msimang has already said he was approached to contest Trollip.
Western Cape Education MEC Debbie Schafer and Free State chairperson Annelie Lotriet are also among those said to be considering contesting Trollip.