Land Rover Repair: LR Disc-II P1590 error, vacuum leaks, engine sensors

Question
My wife's Discovery-II isn't idling well and intermittently has little/no power to move the vehicle.  a P1590 code is showing on the reader.  Where do I begin looking for the problem?

thanks.

Answer
P1590 has nothing to do with engine running.  You can look for vacuum leaks, check plugs and wires, and clean the throttle body to try to improve idle.  Beyond that you need a factory level test system where you can look at the roughness signal and see which cylinders are rough, and you can hopefully get some idea why you are losing power.  The code you have is probably irrelevant to that issue.

People often incorrectly assume these codes have all the answers but in truth the answers are more likely to be found in the live data stream, where you can look at the readings from all the engine sensors as the truck is running. That's where I would go first.  We use a factory scan tool but several aftermarket tools show this data as well.

Good luck with it all

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John Elder Robison