lambda/o2/hegos sensor

i'm having a bit of bother with my 95 3.9 v8 disco, she keeps going into 'limp mode'

my question is would blocked or gummed up catalysts throw the lambdas out enough to put her in 'limp mode' and would a knackered lambda have the same effect???

or am i barking up the wrong tree??

should i be looking else where?? is there a common fault(s) that would put a v8 disco into limp mode...

Don't guess get the ecu fault read

Cost me £35 to have a tuning guy check out the sensors and diagnose my problem as a knackered fuel pressure regulator.

Basically he checked the temp sensor, both lambda's, MAF, ECU and injector timing.

Was running so rich that the ECU couldn't reduce the injector timing any further, and got totally confused. Failed MOT on lambda but there was sod all wrong with it.