The throttle position sensor (or TPS as it is called), is nothing more than a potentiometer where over a gradient range from 0 to +5V a moveable arm reads out the position of the engine throttle lever. It appears to be the same unit in all Diablo cars. I do not know about the more recent cars.

 

The sensor is connected to the engine throttle control by two screws. These screws can loosen causing the engine to have a high RPM on idle and/or have the carter motor remain on after the ignition is switched off. The latter will run down the battery overnight.  Alternatively the TPS itself can ware out giving back unreliable  information about the engine throttle control to the LIE computer. Fortunately checking and adjusting this sensor is simple.

     Figure 1

While it is possible to remove the sensor itself without removing the engine throttle control unit, it is difficult to get it back on properly and very difficult to adjust the settings as described below. It is best to take off the whole air intake valve unit and work from there.

 

So first remove the right hand rubber air duct hose to the intake valve manifold by unscrewing the two hose clamps.  Also you will need to remove a small connecting hose at the side of the manifold.

 

      Figure 2

Next remove the two screws that hold the sensor in place. Then disconnect the 3 pin electrical connector to the sensor. To do this you must pop out the wire spring clip of the connector. Use a screwdriver.

 

Check the connector is OK. Look for any corroded pins or bent pins.

 

 

 

 

 

    Figure 3    TPS socket connection

Next remove the 4 nuts that attach the engine throttle control to the air intake manifold. The bottom two are hard to get at. You need a box spanner wrench.

 

Gently tap on the unit to get it off. Take care, there is a gasket between the two metal joints.

 

 

 

  

 

      Figure 4  Removing throttle unit

The sensor is connected to the engine throttle control via a rotating rod that has a flat edge on it. It is tightly attached to this rod and need patience working it off.
 

 

 

 

 

 

 

    Figure 5   TPS removed from throttle unit

The throttle sensor itself (Lamborghini part # 001327641) is made specifically for Lamborghini by Weber. (It costs ~$170). It should be checked out to see if a replacement is required. 

 

 

 

 

  

 

 

   Figure 6.  A TPS unit

It has a 3 pin connection. Each pin is marked on the unit a,b, & c. Just like any other common potentiometer is consists of a layer of high resistance material  from pins a to c. The resistance from pins a to c should be 600-700 Ohms.

 

A rotating arm moves along this gradient of material with a to b resistance of 4 to 600-700 Ohms. (The resistance for b to c should correspondingly go from 600-700 down to 4 ohms).  This can be done by clamping the unit is a vice and using a screwdriver to rotate the control in the center of the unit

 

 

      Figure 7.  Measuring TPS sensor readings

Now to adjust the unit you need to attach the sensor to the engine throttle control unit. Measure the resistance across pins a and b. And rotate the sensor on the housing such that with the intake valves fully closed the resistance is about 4 Ohms and with the valves fully open the resistance goes up to 700 Ohms. The resistance should rise smoothly and gradually as you open the throttle lever. It should not jump to 200 ohms on say a slight opening. If it does the internals of the sensor are worn and a new one will be required.  Note. It was reported to me that on an earlier Diablo model, the fully closed resistance was 90 Ohms.   Clearly some experimentation will be required for your car. Try rotating the TPS position slightly to get the RPMs to 1100-1200 without pressing the accelerator pedal.

 

    Figure 8. TPS attached to throttle valve unit (removed from engine) for calibration.