Fluctuating lipase numbers, negative mrcp, ercp, CT scan. Numbers mainly normal but sometimes elevated for no reason. Lung cancer?

Not likely. Elevated lipase does not suggest lung cancer.If amylase is normal and all the tests you describe are normal.What that means is you do not have gall bladder disease, pancreatitis .If lipase is elevated sometimes only i will not worry follow up with your doctor/gi specialist.
Symptoms. Proper medicine won't treat #s only but the person as a whole. What are your symptoms? If the lipase elevations are mild and asymptomatic, they may not be of concern if everything else is normal. If you've not been seen by gastroenterologist, you may consider that, too.
What diagnosis. Are you searching? Do you have any symptoms? Is there a real reason you think you have lung cancer. Why are you having so many lab and imaging studies?