Hi i have a problem with a landrover which has had a V8 transplanted from a discovery 1996 fitted with lambda sensors, when the engine was transplanted by the previous owner it ran fine , it now has developed a fault of poor idle , if the revs are brought above 2000 rpm it clears and will run great and rev untill it drops below and then misfires and idles unevenly. ive checked all pipes and replaced the cap plugs and leads. I do know that the previous owner never fitted the speed sensor from the discovery but as i say the vehicle ran fine for a good 6 month before the fault occured, how essential is this speed sensor ??? after reading other threads the throttle position sensor i am goin to swop tommorow , can anyone shed any other light on this problem? Thanks

I had the same problem and it was the idle control stepper motor that was dirty. It sits at the back of the plenum chamber.