Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing plus 8 r380 gearbox speed sensor

Hi all,

I have once again got the dreaded engine idling issue on the V8, and there are only three items that I have not as yet replaced (as far as I can think), these being the Gearbox speed sensor, the ECU and the O2 sensors.

When I bought the mighty 4.6 V8 1997 plus 8 seven years ago I fought with the idling issue for some time, ie stalling at lights, and erratic idling in general. I gradually changed all the parts, but no one thing seemed to resolve it. However after replacing most the related parts the problem went away!

I thought I had cured the problem by fitting a new air idle valve, new Airflow meter, new throttle position sensor, Tornado chip, Bosch injectors, new coil and RPI spark improvement device. I even fitted a new fuel pump, and ignition trigger in the dizzy!. In addition to resolving a number of vacuum leaks.

These mods seemed to solve the issue with only the occassional rare poor idle speed which I learned to live with.

But now the problem has returned, in that the idle speed after start up (only when the car is moving) remains very high until the car is at standstill, in which case it drops to the correct idle. After about three or four stops at traffic lights the idle speed then performs correctly for the rest of the journey.

However if I stop the engine the problem then resums untill I have stopped at three or four traffic lights. Very annoying.

It seems like the ECU learns to reset the idle somehow?

I have fitted another new Air Idler valve, (no improvement) and I can only think the problem may be the gearbox speed sensor or the ECU or the O2 sensors.

I am going to fit one new O2 sensor soon, as I can see that the even bank exhaust pipe is black with soot and the odd bank is perfectly clean, so I assume one of the O2 meters is playing up, giving the even bank a richer mix, and this may indeed be the cause of the erratic idle, who knows?

Has anyone figured out where the R380 gearbox speed sensor is, as I would like to check it out. I think it is an electronic type sensor as (if my memory serves me right) saw some wires coming out of the off side of the gearbox, which I assume is the electronic speed sensor.
I have also noticed that sometimes I get strange and erratic readings on the odometer, which I think possibly takes a signal from the gearbox speed sensor.

Anyone know anything about this electronic speed sensor, I assume it is a pulse device similar to a modern ABS sensor? Any help would be great.

I can only find info on the mechnical type gearbox sender, but I dont think this is the same device.

Just thoght I would ask the Forum guru before I get the car on jacks and start poking around!!

Are you referring to the Road Speed Sensor (Transducer)? I realize that my 94 +8 is not the same as yours but my Road Speed Transducer is mounted on the fire wall where the transmission tunnel starts. The easiest way to find it is to follow the speedometer cable back from the dial and you will come to the little box, the wires on my gear box are for the reverse light. The Road Speed Transducer would not cause erratic idle but would cause stalling when coming to a stop.

There's a sensor pick up on the bottom left of the R380 box, which can cause erratic idle if it comes loose or is misaligned somehow, I believe. I recall researching it on other Landrover forums when I had issues. My problem ended up being the throttle postion sensor. I used a cheap pattern one to start, which didn't improve things, but after fitting geuine LR part it seems to have been fine over the last 40k miles or so. You could try unplugging the TPS and running on MAF signal alone. That was how I found the problem.You won't have the performance response, but the engine should idle fine.

Good luck, Phil

If you have a mechanical speedometer the speed sensor is a small device screwed to the bulkhead and the speedometer drive from the gearbox comes up to the sensor, then there is another speedometer cable from the sensor to the speedometer. In the past my 3.9 had stalling issues which were due to loss of the power to the heaters in the O2 sensors. I did have to change the O2 sensors at one point as one of them was getting lazy and causing one bank to run rich.

Thanks kindly for all your replies.
Mine does not have a mechanical speedo, it is electrical and yes I am referring to the gerabox speed transducer .
I have checked the TPS on my multimeter and it appears to be fine, however your tip is good and i'll try it.
I have also checked the water temperature and fuel temp sensors and all appear to be good.
Ill get the car up on axle stands and check the transducer as soon as I get a chance.
Ill report back with the findings as I get them.
Many thanks to all, great forum chaps.