My 2002 x type jag not going beyond 3000 rpm and idles rough

 

Hi,
I am assuming it is a petrol engined X type.
Check the breather pipe that runs from the cam cover to the inlet manifold as it usually splits and causes an air leak which is too much for the ecm to compensate for and to prevent engine damage it reduces power at @ 3000 rpm (feels quite violent when 3000 rpm is reached).

Hope this helps.
Gary

 

I have the same issue, fine on a long or short run but when I stop at lights or in traffic it will go into what feels like super limp mode, however no codes and it does clear itself when I am slowly able to get up to speed, no idea what is causing it car has a new diesel filter and recent service, it is intermittent but can be dangerous particularly if pulling out from a busy junction. Any help appreciated