It came on this morning on my way to school. Noticed that when put in park, it wouldn't stop accelerating and rpm slightly increased. I do know the head gasket needs replacement. Also, sometimes parks just fine without any check engine

 

Ok so I turn it off for a few mins and start it back up. No more check engine or weird sound/rpm. Wtf?

 

I would have the code ran, that more than likely should tell you what it is. Depending on what year the Cherokee is, you may be able to get the code by turning the key to accessory a few times, and then the code would show on the dash. My 04 Grand does this.

 

He's got a 95 Grand Cherokee with the 4.0. It could be a vacuum leak somewhere causing the RPMs to go up but I have no idea about the CEL. You can cycle the key on and off 3 times, leaving it in on the position on the 3rd time. The CEL will start flashing, count the flashes.

Example, flash, flash, flash, pause , flash, flash. is a code 32

or, take to Pepboys or Autozone and aske them to read your codes. The OBD connector should be by your battery or near the coolant overflow tank under the hood.

Let us know what happens.