Several years ago, I wrote an article for the magazine relating to electronic throttle body operation and how to get yourself out of trouble if hit by failure of the unit. In broad terms the article was written specifically with the petrol S-type V6 and V8 as the basis for investigation but a similar unit can also be found on petrol X-types and also in modified form on the later models and petrol X350 and XF models also.
Prior to writing the article, my car suffered repeated limp home failures due to a previous owner or his garage having struggled to remove and breaking the fly by wire plug from the socket linking the drive electronics to the sealed Throttle Actuator Control (TAC) module on the throttle body. Only by moving the plug within the socket, could I get the throttle to behave correctly. Failure would occur again soon after and the saga would repeat until I finally lost patience and bought a second hand throttle on ebay for just £25. A true bargain if ever there was one because new replacement only from Jaguar would today cost in the region of £1500!
The issue with this electronic throttle is that if problems occur with the TAC module or the stepper motor, neither is replaceable on its own. The two components are matched to each other at the factory and individual replacement is not possible. The only salvageable unit on the throttle body is likely to be the throttle plate position potentiometer which may be switched between throttle body units. The new price of this individual component is around £87 on eBay.
How to get around the problem? Several alternatives present themselves, buy new, talk to BBA Reman about the possibility of an overhauled unit or buy second hand. The going price from a breaker is around £120 - £150 with usually a short warranty. From private sellers typically on eBay, the price is more likely to be between £25 - £60 for a unit which is said to be fully working.
Replacement is easy enough with just the inlet trunking to be displaced and four long Torx bolts which secure the throttle to the inlet manifold. A special gasket is needed to mate the throttle and manifold together and the gasket is generally around £9 in price. It is essential to replace this item as the old gasket will disintegrate when a throttle is removed from the inlet manifold. The throttle body will often be choked with crank case breather residue. This needs to be cleaned out with a soft rag and preferably carburettor cleaner to dissolve deposits. I`ve found acetone also works well. Ensure the throttle plate and its edges are clean and also the bore of the throttle body itself. This will help good airflow at idle and allow the engine to idle smoothly.
The other day another second hand throttle body came up on eBay at a reasonable start figure. no one else seemed interested in it and I decided to buy the unit in the last few seconds of the auction. This unit came to me for £25.50p. Such is inflation. The throttle arrived this morning but I noted the throttle potentiometer had been interfered with. No matter though as I had the original pot still remaining on my original old throttle body so I swapped it over onto this latest acquisition. having cleaned out the throttle as described above, this unit goes into my stores just incase the throttle currently on the car gives up at some time in the future. in the meantime, short of removing the current unit from the car and substituting it for this new item, I have no real idea as to whether the unit is in serviceable condition. For such small money, it was worth a punt.
A few images now.
The two throttles on the bench, one with broken electronic circuitry, the other with a damaged throttle potentiometer.
I believe it is well worth hunting down this type of unit to have as a spare part. In years to come supplies will start to dry up and obtaining a replacement part may become difficult and no doubt increasingly expensive. We can never have enough cheap spares!
Mike