Land Rover Repair: 96 Disco idles but wont rev, engine sensors, correct direction

Question
Hello John. You always seem to have some insight so I hope you can point me in the right direction. I have a 1996 Disco 4.0 with 132000 miles. We drove it on a 120mi trip and then parked it for a few days. I went out this morning and it started and idled fine. When you try to rev it, it will go to 1200 rpm's fine at 1500 it starts to backfire possibly through the intake, and you can get a max of 1700 rpms. It sounds like it is working pretty hard to get there. If it were an older car it sounds just like the choke is stuck closed(I know it doesn't have a choke). We are fanatics about oil changes and the Rover has never had anything but premium gas to try to keep the valves from getting carboned up. The truck had fuel pump about 10,000 miles ago, but I can't remember if we changed the filter.I also do not have a check engine light. Do you have any ideas what would cause this problem? Thanks Patrick


Answer
I'd suggest checking the fuel pressure (should be 40psi or so) and spraying a mist of water on the ignition wires to see if they spark.  Beyond that, I'd connect a scanner and look at the live data from the engine sensors and see what readings are out of line.  The data should point you in the correct direction.  

Note that low fuel pressure won't set a code so you have to manually test that, and misfiring from wire breakdown is best found as I described here.