Let me try to help with this.
An Engine misfire In the engine, if running poorly enough, YES that code could set and not clear or Reset soon after clearing. I found that in writing for you contained below. I don't know how rough your engine is running, but it is possible the inability to clear is tied to poor or unsable Idle quality due to the leaking valve..
If the engine is still running relatively smoothly, then there could be a problem in another system but the code still appears as the P080
Keep in mind that a lot of these systems run on the same circuits and anything can cause anything basically. But the information below will be very important to take into your Cadillac Specialist.
I'd really like to know what a scan tool reading looks like on your vehicle.j I'd need to see the entire picture of all parameters.
I think you'll solve your problem with the information I found for you listed below.
NOTES ON FAULT TREE
If Code P080 does not change to history following the completion of the TP Sensor/Idle Learn Procedure, this may be due to incorrect or erratic signals from the following sensors:
High electrical loads may disable TP Sensor/Idle Learn. Components that may produce a high electrical load are the headlamps, the rear defogger, high HVAC blower and the cooling fans. If difficulty is encountered learning TP Sensor/Idle values (i.e. Code P080 remains current), turn "OFF" these high electrical loads. Also, it is important to accelerate the engine above 1000 rpm after turning "OFF" the above components because the PCM will think it is still under a high electrical load until it checks the system again (when engine rpm exceeds 1000 rpm). Furthermore, since the cooling fans cannot be manually controlled, engine coolant temperature must be below 105°C and A/C refrigerant temperature must be below 51°C in order to turn "OFF" the high speed cooling fans and their high electrical load.
Code P080 may also remain current if the idle is rough or unstable. Correct problems with these sensor's signals or the idle before attempting to perform the TP Sensor/Idle Learn.
Hope this is what you are looking for.
Keep me posted