Also, if you take off the duct to the MAF going into the intake throttle body, then looking straight into the metal throttle body you will see the throttle plate that rotates AND on the bulkhead side, you'll see a little port hole about pencil size. That's path allows air to bypass the throttle plate at idle no matter what. That can get clogged up with gunk. When I had my D1, I would take carb cleaner with the long straw, stick it in there and spray until the splashback fluid would come out clear instead of dark brown.
That and/or the stepper are likely your problems. ECU controls the stepper, which controls your idle.
Are you getting any codes? Another possibility is the road sensor or speed sensor. The speedo cable connects to it right before the transfer case.
94D90 NAS 3.9 LT77 LT230T Soft Top
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i had similar symptoms and it turned out to be an old vacuum hose between the intake and fuel regulator. the rubber had expanded it was pretty loosely connected on one end. lamorna in seattle fixed this today for me and reset the base idle, so far so good.
The one you posted converts from a lower speedo cable attached to the transfer case to an upper speedo cable. Not sure why Land Rover used this method on NAS trucks, it seems like a really complicated and expensive way to do something very simple. Eventually Land Rover wised up and used a hall effect sender only.
The YBE100530 is a hall effect sender only with no upper speedo cable. It is designed for electronic-only speedometers and installs directly to the transfer case.
Land Rover then replaced the YBE100530 with the YBE100540 which is basically just another hall effect sender. The main difference is that the ***540 unit is a cheezy plastic piece of crap while the ***530 unit is better built unit. It saved Land Rover some money, but the difference in build quality is substantial.
I replaced my old school mechanical speedo cable with the YBE100540 unit, it's yet to be seen if the cheezy plasticness of the sender is a liability.
Also Overlander, you mentioned a couple of things that sound extremely helpful, and fairly easy to try and fix for us DIY guys. Any chance however you can try and give us a better indicator where the throttle body is inside the hood. I am all the sudden getting some of this stall of which you all speak. Also any help located the "stepper" would be greatly appreciated.
picture attached of removed throttle body. look inside and you'll see the hole on the inner wall with a hose coming out the outer side. that let's a small amount of air bypass a closed throttleplate so the engine will keep running if the stepper can't keep the throttleplate open itself(because it failed).
Also attached pic of stepper motor location from landroveronly.com. stepper motor (aka idler valve) is clearly marked with arrow. you can find an equivalent part for a corvette. don't remember number but it's a common sourced part at any autostore. disconnect 2 wire connector, unscrew it and install new one with new o-ring.