Engine idles rough slightly when hot There are no stored codes upon scan,

A rough idle would probably result in a Malfunction Indicator Lamp (MIL or Check Engine) and one option would be to go to an auto parts store and have them read codes stored in the On Board Diagnostic (OBD) system. Before doing that however, I would pop the hood and with the engine idling, carefully, carefully wiggle all the vacuum hoses you can see. Split or cracked lines can introduce "unmetered" air to the intake system, leaning out the mixture and causing your symptoms.

Of course a defective Exhaust Gas Recirculate (EGR) valve, as well as other failed or failing engine management devices can also cause idle problems and that's where the code scan can help. But don't expect a scan to pinpoint your problem. Code interpretation is an art.

Other options:

Dirt around the throttle plate.
Ignition system issues.
spark plugs (although problems here do not usually present at idle)

Go for the low-hanging fruit first, loose or defective vac lines.

All the best.

have the codes checked if you haven't as it can store a code without check engine light being on. You may have a headgasket seeping .

if that is engine related, we dont know here , we cant drive it and feel it.
if that was engine vibration, its most likely MISFIRE.
the #1 cause of MISFIRE, is not doing the 60k mile tune up.

is the CHECK engine lamp off driving? if not scan the ECU/PCM
any scan tool works. (new types) even a $9 tool.
scan it for P03xx codes, misfire.

rough hot or cold engine.
rough only driving and not at idle and not racing RPM parked?
does engine ever stall>?

CODE SCAN VECHICLE SOUND LIKE SEVERE CYLINDER MISFIRE, COULD HAVE BAD SPARK PLUGS OR WIRES.BAD IGNITION COILS,COULD HAVE DIRTY FUEL INJECTORS,SLIGHTLY CLOGGED FUEL FILTER MANY THINGS WILL CAUSE MISFIRE BUT CODE SCAN VECHICLE SEE WHAT CAUSING ENGINE MISFIRE.

If the engine seems to run fine over 1450 RPM maybe there is a vacuum hose leaking or EGR valve is slightly stuck open. Any help from the OBD II trouble codes? Or is there simply no MIL and no stored information in the OBD II computer read at the local parts store through the connector by the drivers knee?

Take it to a auto parts store and have the computer scanned for the trouble codes. Autozone will do it for free, then you will have a better idea whats going on. It could be a number of things causing rough idle. I would get it scanned before replacing anything else. I hope this helps.

If the check engine light is on, take the car to an autoparts store and have them scan the computer for any faulty codes that it has stored. Most parts stores will do the scan for free. It sounds like a faulty idle air control valve, but getting the codes will identify what faults the computer has noted and in what systems. Hope this helped and best wishes.

It sounds like the timing belt is off a tooth. Did you have it scanned to see what code was in the computer? These engines will surge when the cam timing is off.

Bring the jeep to a parts store and have them read the engine code(s) stored in the computer. The engine light on indicates a problem, and this is the best way to figure out what's wrong. Most stores will check for codes for free (they plug a scan tool into the port under the dash to 'read' any stored codes). Write down the code #'s and ask them what they meah and how to fix the problem. If u have any further questions, u can post them here. Let me know how u make out.

U need to have the engine trouble codes read. Most parts stores provide this service for free. They can recommend what should be done to fix the problem after they scan for codes. Any further info needed, u can post any ? here.