Based on what you described, it sounds like the base idle speed is too low. At an idle, what does the tachometer indicate as far as RPM's? I suspect it could be related to the idle air control valve (IAC) or even an engine vacuum leak. The IAC is what is responsible for maintaining idle speed. Also, it adjusts when an added load is placed on the engine such as AC and turning to maintain idle speed.
What I suggest is to first confirm there are no engine vacuum leaks. Here is a link that explains how to locate and repair a leak:
Next, here is a link that explains how to service the IAC. You can try this to see if it is a contamination issue.
If you find the IAC is bad, here is a link that shows in general how one is replaced:
Here are the directions specific to your vehicle. The attached pics below correlate with the directions.
1996 Land Rover Discovery I (LJ) V8-4.0L
Vehicle Powertrain Management Fuel Delivery and Air Induction Idle Speed/Throttle Actuator - Electronic Service and Repair Procedures
IDLE AIR CONTROL VALVE
(Numbers seen within image reflect procedure step numbers)
1. Disconnect battery negative lead.
see pic 1 below
2. Disconnect Idle Air Control (IAC) Valve multiplug.
3. Remove 2 bolts, remove IAC. Discard gasket.
4. Ensure all mating faces are clean.
5. Using a new gasket, fit IAC. Secure with bolts.
Tighten to 2.3 Nm (2 ft.lb.)
6. Connect multiplug.
7. Reconnect battery negative lead.
I hope this helps. Let me know if you have other questions.
Take care and God Bless,
Tuesday, February 23rd, 2021 AT 6:56 PM