what would cause my jeep to idle up and down under a 1000 rpms to like 400 moving about 200 rpms and everytime it sounds like its missing but runs ood when gas is applied.Doesn't start in the cold unless you give it gas and then it idles a like 200 or 300 rpms until getting warmed???The motor is the older model 4.0 with gray valve cover we swapped the old intake offf the high output motor and the header.

 

You still have a CEL what codes are you getting?