Hey guys, new to the forum but been reading religiously since we purchased this Disco a few weeks ago. Having idle problems and stalling.

1995 Discovery 1 3.9L V8 (No cats or O2 sensors) Automatic gearbox.

The issue is more prominent when the engine is warm. The car seems to drive fine under normal conditions, but when coming to a stop in Drive at a red traffic light, the revs will dip up and down then sometimes stall. In addition to this, If I quickly stab the throttle at idle it will stall every single time as the revs fall back down it will not pick back up in time before it stalls. The idle also feels slightly rough. A strong fuel smell is also present.

So far I've cleaned the MAF, cleaned the IACV, checked for vaccum leaks, new spark plugs, checked timing with no difference. The idle still hunts with the IACV unplugged.

Now here's the weird part, unplugging the Coolant Temp sender will instantly bump up the revs a tiny bit and it will idle perfectly. Stab the throttle and it returns the idle perfectly. As soon as I plug the coolant temp sender it starts to idle like **** again. The temp sender itself appears fine as its around 280 OHMS when at running temp.

​​​​Any ideas are greatly appreciated guys. I'm losing sleep over this one.

 

It's probably in some kind of limp mode since no O2s. Are there ports for the O2s or only straight pipe? The O2 sensors are at the heart of A/F ratio hence injector pulse width. Will get around 9 mpg with O2s unplugged, but near 13 mpg with working O2 sensors. So, it's worth fixing the O2s if you can.

Other than that, we'll need to check base idle, and ensure the throttle plate adjustment is perfectly centered (same measurement top and bottom). There is a factory adjustment on the MAF to bias fuel at start up, but that's probably the last thing to check.

Could also be related to fuel pressure or the fuel pressure regulator. That might explain the smell, but isn't likely since it perks up when the CTS is unplugged. Check the vacuum connection is correct to the fuel pressure regulator. There are a few vacuum lines back there that are easy to get crossed. Can you drive it with the CTS unplugged?

Make sure the PCV oil trap, hoses, tee, and orifice are all good. AB sells a nice tune up kit for these.

I had trouble with my vacuum advance mechanism. The diaphram failed. This causes a small vacuum leak. Try plugging it off near the throttle. If you ever replace it, make sure you get the one for the 3 pin amplifier (it costs more). The cheaper one looks the same on the outside, but changes the timing in a different way. Maybe plug off the charcoal canister too. The idea is to eliminate possible potential errors (e.g. vacuum leaks) (there really aren't many to cap off).

Have you checked for codes? There's a display under the passenger seat with 2 digit red numbers (looks like a black box if no numbers are lit). I found the code meanings on line. It only shows one at a time. Is the check engine light on?

This truck is really super simple, so don't worry, you'll get it going.

 

Get a new coolant temp sensor. They are cheap. https://www.roverparts.com/instruments/sensors/ETC8496/