Hi Im working on a friends 1996 Land Rover with the 4.0 engine. The problem is when started from cold, it will randomly surge between around 500 rpm to 2000 rpm and also stalling, unless I hold my foot on the pedal to keep it around 1000. The problem goes away when it warms up. Im thinking that when the car is cold the computer runs open loop and the only sensor it uses in open loop is the coolant temp sensor? And since the idle surges between the 2 extremes I listed, I dont think it's the temp sensor.

I also though it may have a leaky head gasket, because the heat doesnt blow very hot when engine is warmed up, and you can feel the heat get hotter when you raise engine rpm, and colder when you let your foot off the pedal. But, Im not seeing any exhaust bubbles in the coolant, and smoke from the tail pipe is only slightly white during warm up then goes clear when warm. Car has a 195 degree thermostat


recently he had accidentally put in motor oil for a diesel car, which he ran for about a week until I found out. I noticed a lot of carbon build up in the valve cover breather tubes, so I cleaned out the fittings and replaced the hoses, then I used the AC Delco upper engine cleaner by taking off a vacuum line from the throttle body, draining the bottle into the engine until it died and left it for 24 hours before starting it back up.To flush out the lower end I added gunk motor flush and ran at idle for 5min then drained oil. Replaced with 10-30 partial synthetic.

He was experiencing the stalling before the diesel oil incident, but now it's worse.

Hoping some land rover enthusiasts could give me a little insight and direction, thank you in advance

 

Clean the IACV.

Diesel oil has no effect on these engines (or any other). Most of us are using Rotella T5/T6 or Valvoline 5W40. You dumped perfectly good oil. Make sure every vacuum hose is connected (well) to the plenum and clean the passenger side valve cover oil separator which is the PCV. There are two coolant temp sensors, one for the computer and one for the idiot gauge. Neither are your problem.

 

I will check the IAC, and should probably just take apart and clean the throttle body anyways. But, if the IAC is causing the problem, wouldnt it happen all the time at idle no matter if its cold or warm??

 

I have the same problem with my 96 disco. I'd love to know what causes it I've given up .