why does my jeep idle so high at 4 when parked and blow black smoke out of the back of the engine

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! Your Grand Cherokee's high idle and black smoke show might be turning heads for all the wrong reasons. The conundrum is: Why is there a high idle, which sounds like a vacuum leak but is also burning too much fuel? When we researched this, there does seem to be an issue with the IAC (Idle Air Control), but what's burning all of that fuel? Well, there may be an answer! There's also a history of failed PCMs, which may not allow for compensation of the air/fuel mixture. The best way to figure this out is via a pro! Take it to a shop, especially one with expertise in the more vintage Jeep area! If you need any further advice or if you'd like any help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554.