P38A problems with engine idle and exhaust

the story so far......so having returned from my stranded in slovakia issue then again in bulgaria i have just bought a p38a range rover 4.6 v8 (yes i know its filled with problems) going was good for the first 2000 miles then the centre exhaust box exploded from a misfire / unspent fuel issue. fixed the box to return normal back pressure then changed plugs and leads. it still missfires but now at idle revs (in park or neutral) decides to idle at 2000 rpm!?!?!?!?!? what could cause both these problems simultaneously or are they just coincidental????? i am eternally greatfull to any who contribute. 300tdi alex

it should still run without exhaust causing too many issues so long as lambdas are working, check the wires to these and (someone will be along to tell you how) check lambdas are ok. obviously plugs need checking but they are new so prolly rule that out, also maf sensor can be destroyed after a backfire.

check leads are on correctly and firmly on each plug.