Vehicle Speed Sensor

[westonben]

Hi all,

Newbie here! Just got a 1999 Series 1 Discovery Auto V8 3.9. It' s got an idle problem. 104k km's (c70k miles)

Pulling up in trafiic/lights etc. the revs can drop to the point of stalling and then may recover. Had all sorts of parts replaced: fuel pump, Air Mass Sensor, Temp Sensor, replaced all filters, cleaned throttle body and idle control valve. Problem is better but still there.

Searching the internet, I keep coming back to the Vehicle Speed Sensor (is that the same as the throttle position sensor??). There seems to have been some good write-ups to replace this part, but they don't seem to work any more. Can anyone send me a write-up to replace it or is there a way to test whether this is my problem?

I believe the Throttle position sensor is part of the Exhaust Gas Recirculation System whereas the VSS is part of the Fuel injection System.

Can anyone help? Not even the dealer has been able to diagnose the fault and I'm now getting disheartened.

Thanks

Ben

 

[joey]

I don't think your issue is the VSS, but I could be wrong.

The VSS tells the ECU how fast you are going, when it goes bad, the engine will seem to lose all power normally about 50 mph, quick test is to change to 3rd gear vice Drive (4th) when it happens, if it goes away it is the VSS.

Your issue sounds more like the TPS which is located right next to the IAC, the TPS and IAC are literally right next to each other. If you clean them both and the issue is still there, I would change the TPS out first.

 

[westonben]

I think it's possible to test the TPS with an Ohm Meter (I think I read). Will dig out the manual tonight and take a look. Thanks for the help.

 

[westonben]

The more I read the more I'm convinced it's the TPS. Problem is I can't locate the sensor. I'm not so good with engines to be honest! Can anyone help with a diagram or picture?

For anyone having a similar problem here is what my repair manual states to test the sensor:

This sensor is only used models with a conventional fuel injection system asn is location on the fuel injection pump.

TESTING
Start the engine, and run it until normal operating temperature is reached.
Stop the engine and diconnect the throttle position sensor wiring plug.
Connect the ohmmeter across pins 1 and 3 of the wiring plug. The reading should be 1000 to 1050 ohms.
Connection the ohmeters between pins 1 and 2 of the wiring plug. The reading should be 850 to 900 ohms.
If the readings are not as specified lossen the two sensor retaining screws and rotate the sensor to achieve the correct readings. Tighten the retaining screws when the readings are correct.
If the correct readings cannot be obtained by rotating the sensor then it is faulty and should be renewed.

 

[westonben]

TPS is only on the diesel models. The part on the fuel injection system is the Throttle Potentiometer. Anyone know of a way to test the potentiometer without buying a new one?

 

[joey]

The below info comes from the Land Rover Repair manual in the MPI Section not the TDI section.

Also it is located in the picture via this thread:

http://forums.landroverworld.org/showthread.php?t=2133


The throttle position sensor is mounted on the side of
the plenum chamber inlet neck and is directly coupled
to the throttle butterfly shaft.
The throttle position sensor is a resistive device
supplied with a voltage from the ECM. Movement of
the accelerator pedal causes the throttle valve to
open, thus rotating the wiper arm within the throttle
position sensor which in turn varies the resistance in
proportion to the valve position. The ECM lengthens
the injector open time when it detects a change in
output voltage (rising) from the throttle position
sensor.
In addition the ECM will weaken the mixture when it
detects the throttle position sensor output voltage is
decreasing under deceleration and will shorten the
length of time the injectors are open.
When the throttle is fully open, the ECM will detect the
corresponding throttle position sensor voltage and will
apply full load enrichment. This is a fixed percentage
and is independent of temperature. Full load
enrichment is also achieved by adjusting the length of
the injector open time.
When the throttle is closed, overrun fuel cut off or idle
speed control may be facilitated dependant on other
inputs to the ECM.
The throttle position sensor is ’self adaptive’, which
means that adjustment is not possible. It also means
the throttle position sensor setting is not lost, for
example, when throttle stop wear occurs.

 

[westonben]

Thanks, I'll swap it out and let you know if it's fixed the problem.