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In this car the circuit opening relay is mounted next the ecu behind the glove box. Opened it up and realised it was not engaging. I engaged it manually and finally got power to the FP relay. Now to solve the hunting idle.

Well, pkyanko, if it is any comfort, I am an idiot too. So don't feel like you are alone. I just pretend to know and so far, it has worked. An engine code 31 for your year LS400 means that the air flow sensor is not behaving correctly as far as the computer can tell. The VAF stands for Vane Air Flow. Most people call it a MAF (Mass Air Flow) which it is in later models. The VAF works by the incoming air moving a vane which is hooked up, mechanically, to a sensor which feeds the computer. I would start by examining the connector to the VAF. As cars age, connectors become highly suspect as corrosion sets in. There are cleaners, such as CRC contact cleaner, made to clean up connector terminals and pins. There is also the possibility that the pin has vibrated lose from the VAF circuit board inside. That happened to my 92 ES300 but I able to take the air flow module apart and resolder the connections. If cleaning and reseating the connector does not help, I would check the resistance of the air flow sensor throughout its range of positions. You will need to remove the air flow unit and will need an ohmmeter to make the measurement. You *may* need to buy a new or rebuilt air flow unit if yours proves defective. They are not cheap (read: hundreds of $$$). Here is some additional reading material so you can brush up on how the unit works -> http://www.autoshop1...m/forms/h34.pdf