I'm not aware of any "liberal mainline churches" that are Pentacostal. The Assemblies of God is the largest Pentecostal church and is by no means a liberal mainline church.
As a matter of fact, it actually started down here in the Bible Belt amongst the poorest of people
"Pentacostalism" started in Kansas and had it's first big revival in the Azuza Street Mission in Los Angeles.
I was not referring to Pentecostal churches but to Pentecostalism within liberal, mainline churches (Catholic, Episcopal, etc.). In those cases Pentecostalism always seems to be promoted by the same people who push for Biblical criticism, "social justice," and endless innovation. It doesn't make any sense, but that's the way it is.
"Pentacostalism" started in Kansas and had it's first big revival in the Azuza Street Mission in Los Angeles.
I know about Azusa Street (at which, I'll bit, no liberals were present), but I had heard that Pentecostalism begain with a poor (perhaps illiterate?) Tennessee preacher named George Went Hensley.
Also, the intellecutal assumptions about a paucity of intellectualism amongst Pentecostals has been proven to be utter hogwash by a number of scientific studies.
Most of that perspective came into public consciousness via a bunch of atheist and agnostic sociologists writing decades ago from their own biases instead of solid research.