American Idol Drop Randy Jackson As Judge

Sources connected to "Idol" tell us ... there's some concern among the brass that Jackon is not well-suited for the mentor role ... but they feel they need him because he's the glue that helps keep the show together.

As for his replacement ... sources tell us Nicki Minaj's deal is 99% done ... but still not a sure thing just yet.

We're told the honchos are keenly aware Mariah Carey isn't a fan of Minaj and doesn't want her at the table ... a fact producers LOVE because they think the conflict and tension will be good for the show.

And ... we now know A.I. will once again go with a 4th judge ... we're told producers are gunning for someone from the country music world for the third seat. Seat number 4 is up in the air.