2000 xk8 convertable 81K
This morning, I noticed my accelerator pedal was sticking when depressed. I returned home and manually rotated the throttle body where the cable meets the spring. It was in fact sticking and making a clicking noise. I drenched it with a lubricant and it now works smoothly. I removed the intake hose and inspected the throttle body and found it immaculately clean. (it was replaced about 10 years ago). I moved the butterfly looking to see if it was stuck closed and found it was working but not connected, as I thought, to the large round spring on the outside of the throttle body. WHen cold starting, the car starts rough and idles about 1200 rpm for about 15 seconds then settles down. I've had intermittent issues in the past with amber light restricted performance. Has anyone else had this issue and does this sound like I may need to have the throttle body inspected?
Thanks

 

Go back to the throttle body, wedge it open and use cleaner and rags to clean. Clean it twice then hose down with cleaner. Put all back together and then drive it. Your problem I feel is a sticking butterfly, not a cable.

 

Hose down with cleaner is not acceptable procedure unless the throttle body is removed from the engine. Is that what you were suggesting?

 

Perhaps hose down is a little strong. Wipe and spray is correct. The cleaner evaporates so quickly that only a very small amount enters the intake. I agree that removal of the throttle body is best but this simple procedure will solve the problem for several months.

 

Be careful. The butterfly is not connected directly to the cable. The cable actuates a sensor which tells the ECU what you want to do, and the ECU tells a servo motor to rotate the butterfly. There IS what Jaguar calls a "mechanical guard" which is essentially a fail-safe safety feature, but in slightly simplistic terms, it's a fly-by-wire system.

 

Quite right. As I inartfully tried to explain, I was aware the butterfly was not attached to the coiled spring. I'm assuming the coil spring apparatus which was sticking controlled the amount of fuel, not the mixture. Can I also assume that the electronics that govern the servo motor do not intermittently fail, they either work or they don't? THanks

 

This applies to the earlier engines so may not be exactly the same for yours. For example - cruise control is completely electronic in later engines. However, I assume it isn't too much different :

The electronic throttle enables the ECM to control the flow of air into the engine. It includes:
- an input shaft that receives driver inputs from the accelerator pedal via a conventional
throttle cable
• a mechanical guard, to prevent throttle valve position exceeding driver demand and to
operate the throttle valve mechanically if the electronic system fails
• a vacuum actuator, to operate the mechanical guard in the cruise control mode of operation
• a throttle valve, to regulate the air flow
• a thermostatic air valve, to control a bypass flow around the throttle valve
• a dc motor, to operate the throttle valve in response to inputs from the ECM
• three position sensors, to supply the ECM with the position's of the input shaft (ie.
accelerator pedal), the mechanical guard and the throttle valve
• springs connected to the input shaft, the mechanical guard, the throttle valve and the
drive gear of the dc motor.

Thermostatic Air Valve
The thermostatic air valve is a wax capsule operated valve that enables engine starting at low engine temperatures (with the accelerator pedal in the idle position, the degree of throttle valve movement available between fully closed and the mechanical guard is insufficient to start the engine at low temperatures). The thermostatic air valve is fully open at a coolant temperature of approximately -30°C (-22°F) and progressively closes until it is fully close d at +40 °C (+104°F). A flow of engine coolant through the throttle body provides the temperature source to operate the thermostatic air valve.