Limp home mode

Hi, I'm new to the forum and have been using this and others to rectify issues that I had come with my jag when bought last Wednesday. It is a 2004 x-type 2.1 v6. The guy I bought it off said that there was an issue with one of the CATs hence why the engine management light was on and it was on restricted power (and an odd bubbling sound.) So I bought a obd reader to read the codes just to make sure, low and behold no codes for the cat or o2 sensors. Just a couple of others. P1314 p1316 and p1000. So I whipped out the spark plugs and found one fine, two had oil on them and one of the two was well black (no2 bank codes.) So I swapped out the spark plugs, pulled the rocker cover off and applied a new gasket on a whim to see if that would rectify it. Fault 1316 came back, okay so must be one of the coils. So today I was traveling to pick a new one up (still restricted power but got up to 70) and there was a bang and transmission fault came up on the odometer. Pulled over got her restarted and she set off fine. Got to the parts place, new coil fitted, bubbling gone, ran fine-ish now all of a sudden she's into limp mode, engine restricted to 2nd gear unless on a hill and I have no dash warning lights and the recovery guy couldn't help either. So I was wondering if any of you guys could give me a hand to work this out.

Thanks

Nathan