Also, "defendersource.com" is a good resource for defender issues/questions/used parts/finding repair facilities.

 

Defender 90 NAS engine is same exact engine as the Discovery 1 4.0 Gems

 

I bought a new idle control valve from RN and installed it. It seemed to run smoother at idle, seemed like it had better control of RPM below 1500 rpm. Idled for 15 minutes and all seemed fine. Took it out for a test drive and after a 5 min drive I stoped at a neighbors house and it died. Wouldn't idle, also wouldn't start as battery didn't want to turn it over. I don't know how old the battery is, at least 4 years old and I had a trickle charger on it for 2 weeks before taking it out. Not messing with it any more until I get a new battery for it.

 

Yes, have the condition of the battery checked, and charging system. Typically, the alternator takes over once started, handling all electrical needs of engine components and accessories...and recharging battery. That's why it's weird that this issue shows up after running for a bit. If your battery had a dead cell or shorted plate, it could be causing the alternator to focus entirely on "trying" to charge battery...and it can't because of internal issues of battery. And the charge it had from being on a battery charger is used up in the short drive time.

Is this vehicle on a battery tender or charger all the time, while not being used? You have to be careful, leaving a battery charger on to long, depending on charger, some don't shut off automatically once battery is fully charged...and just continues to cook the battery cells until they are useless.

 

Just checked the battery, it is an Optima Yellow Top group 34. Had to remove the battery to find the date code, L-4. It was not installed in 2024 so I am guessing it was installed in 2014!!... time to replace. Is the group 34 the right size battery? The manual I have says it takes either a 371 or the heavy duty 389 battery, these numbers don't mean anything to me.

 

Update: New battery- started right up, idled fine (700rpm), took it for a test drive. After a 15 min test drive, when stopped Idle would drop to 400-500 rpm and act like it was going to stall sometimes, did stall a few times.
Health issues prevented me from touching it for 2 months. Took it for another test drive today, put in 10 gallons of non-ethanol fuel and took it for a bit of an Italian tune up. First stop was 10 minutes after fresh fuel.... idled at 700 no issue. For the rest of drive, when I came to a stop, it idled fine at 700. In the end, looks like a new idle control valve, fresh fuel and a bit of a hard running seemed to have sorted out the idle issues. Now I have a check engine light on and the code reader I have reads the same codes no matter what vehicle I plug it into. Time to toss it!!
Does anybody have any recommendations for a code reader, or software, that I can use to reliably read the codes on this thing?

 

check the D1 forum for a lot of your questions as the NAS 90 Defender is essentially the same vehicle as the '96 '97 D1 - you might also want to change out your plugs and wires as that can impact your symptoms of idle