XK8 revving when stopped

(Kenneth Wright) #1

My 1997 XK8 has started to rev wildly on occasion especially when stopped. Gets a little scary at traffic lights or stopped signs. Any ideas as to what is causing this? I have no fault lights.

(Neil Bennett. Patron) #2

Could be a worn TPS, I forget what idle voltage should be. It will be in theJTIS or the info on jagrepair.com

(Eric Capron) #3

The output from the TPS at 650 rpm with coolant temperature of 88 degs. C on my 97 car is 0.82 volts. It varies very slightly by 0.01v as idle is trimmed.

If you have access to a scanner or the equivalent that displays live data you can monitor the voltage.

The difficulty of fault finding on a closed loop system is that you might well see the TPS output change as the engine surges and think you have found the problem whereas in fact, the throttle is reacting correctly to a faulty stimulus from some other part of the system, for example a faulty coolant sensor or it could even be a fault in the ECM itself.

The approach I would take is to do the basics such as checking for any air leaks on the induction side, looking for poor or corroded electrical connections in the various plugs, sockets and grounds. Then it’s going to be a question of monitoring the various signals that are available to see if you can pinpoint the cause.

Shropshire, UK

(Kenneth Wright) #4

Thank you Neil for your response to my XK8 speeding up problem. I will try all of the things you suggest that are within my capabilities. The small diameter tube that is attached to the top of the throttle body is broken and I have tried to join it up. Do you think that could be a problem? I am not sure where it goes on the other end. Also the TPS has 4 connections and I expected three. Tough to find a replacement for a 1997.

Thanks again


(Kenneth Wright) #5

Thanks Neil for your response.


(Eric Capron) #6

My car doesn’t have a pipe on top of the TB. I think it is part of the cruise control which I don’t have.