View Full Version : Idle issues

06-06-2008, 01:48 PM
I am not sure If I am doing this right, because I am new here, but I need some help figuring out what is wrong with my 94 Discovery. I runs pretty ok in the morning, but if driven for longer than 30 minutes it begins to idle wierd and then it will just cut off, usually at a red light. It will crank back up immediatly but it is so annoying. It usually only does this when it is warm and hello it is warm in Georgia right now. Anybody that can help I would greatly appreciate it. Thanks Christine

06-06-2008, 04:02 PM
Welcome to the RN forum!

Make sure all your ignition components and air filter are in good condition first, ie new cap, rotor, spark plug wires, spark plugs and air filter. Then, I'd suggest starting with adjusting the air gap and setting the base idle proceedure as listed in our technical tips section. You could take this information to your mechanic or tackle it yourself.


Discovery I

Adjusting Air Gap and Base Idle on 3.9 litre V8 Engine (download 412 KB PDF) (http://www.roversnorth.com/web/downloads/instructions/Base-idle-air-gap.pdf)

Hope this helps, keep us posted.

06-07-2008, 01:19 PM
As Thompson said, the condition of ignition components is critical in the distributor Rovers.

What you have described could be a fouled Idle Air Control Valve, also called the stepper motor, or an overheated ignition amplifier.

Given the fact that it starts right up leads me to believe it is most likely the Idle Air Control Valve.

The idle air control valve is located at the back of the intake plenum (the big aluminium casting with "3.9" cast onto it). Unclip the wiring harness to it. Be careful as it is likely brittle given the age of the vehicle. Unscrew the IAC valve. You will find a tapered piece of metal that mates to the back of the plenum. It is common for carbon to build up on both surfaces. Using carburetor or brake cleaner, remove the carbon build up. It may be necessary to use a scraper, but take care not to gouge either mating surface as that can cause other problems. Do not forget to clean the inside of the casting where the tapered piece seats.

Good luck, if you need pictures, let me know and I'll run out to the shop and take some for you.


ps-much of the work on these trucks is within the capabilities of anyone with the interest and drive to do so. IMO, the '94/'95 Disco are the best and easiest to work on. Mine has 224K miles!

06-07-2008, 01:54 PM
Thanks Paul for adding to this. Stepper Motor is darkened on this diagram, if the recommended cleaning doesn't fix the idle, the link provided below is for a new Genuine Factory Land Rover part. Hope this helps.

RNH654 IDLE AIR CONTROL VALVE (STEPPER MOTOR) (http://www.roversnorth.com/store/p-3420-idle-air-control-valve-defender-90.aspx)


06-07-2008, 05:24 PM
While we're at it, replacing the three hoses in the center of the diagram, the tee piece between them and cleaning the flame trap (the grey canister above the right valve cover) wouldn't be a bad idea either.

Thanx Thompson! Any time, I've got your back!