JAGUAR XJ6 - Sticking X300 Throttle

Q
I have had a 1996 X300 XJ6 since it was new, and the car has now covered 273,000km. For the last three services I reported to the garage that when driving along the accelerator would stick at between 1,500-2,000rpm. When stopped and in Park the engine would then turn over at this high idle speed. The garage firstly said that the butterfly flap was sticking and so replaced the inlet housing saying that the casing had gone oval. At the next service the accelerator cable was replaced and this time they just tightened up the spring. However, the problem is back again. To cure the problem I just have to blip the throttle and the revs go back down to the normal 7-800rpm.
In your X300 owner's guide in the December issue you say that the supercharged cars suffer from oil/carbon deposits on the throttle butterfly, but since mine is a standard 3.2 and the butterfly housing was replaced this shouldn't be the problem.

A
Problems with the X300 throttle housing are reasonably common and while a cleanout can help, sometimes, as in your case, there is no option but to replace. While some housings will simply bolt on and work they should really be set up with a diagnostic computer - was this done?
With the housing and cable eliminated there remains the possibility of a problem within the pedal assembly itself or maybe a section of carpet or trim stopping it from returning. Lastly, the 3.2-litre cars have cable - not electronically - operated transmission, and it is possibly that a sticky transmission cable (to the throttle housing) may be the cause of your problem.