Vigesaa

I've recently had a no start problem with my 99 XJ 4.0 I6. Intermittently my jeep won't start when it's warm. I've noticed it only happens under specific circumstances. After running my jeep and I put it in park on occasion my idle will subtly jump from 700 to 1000 range. After this jump when I cut my engine it sounds kind of rough shutting off and it will not fire back up until it sits for a while. Maybe 15-30 minutes. I figured it could be heat soak knowing thats a common problem with XJs but with the sub freezing temps we've been having and it only happening after this specific idle jump, I'm not so sure. Can heat soak somehow affect my idle? I've recently replaced the CPS and TPS with some cheap aftermarket units from O'Reillys until I can afford some OEM ones. Any suggestions on what it could be? Any help would be greatly appreciated. Thanks