My 2003 XK8 has a slight 'pulsating' throttle when the engine is cold. As the engine works its way up to normal operating temp this wavy steady state throttle seems to go away. The exhaust sounds like the engine is occasionally and intermittently dropping a cylinder while this pulsing is happening. At speed over 40 mph the engine seems to be working perfectly but wind noise and momentum might be masking my awareness of the problem. No CEL or other warnings are thrown. Stand on it and all seems well (no misses, hesitation or back fires). Step #1 for me would be to???
RB

 

The usual answer to this question is get a code reader obd2 and see if any pending codes are present, even if the CEL isn't on.. that will point or exclude many things.

 

I was hoping for one of those, "not unusual, it's usually caused by .......". Reluctantly I'll drive the 15 miles to my nearest Auto Zone and try one of their free OBDII code reads. Thanks for your reply though.
RB

 

...or shell out $10-20 for a wired code reader. better yet get one that will transmit to your phone/computer so you can read live data (also small numbers of $ for a smartphone compatible item).
Next time you might not be able to drive to the garage!

 

There is an issue with the early 6spd torque converters where the lockup clutch will engage and disengage causing a sort of rumble strip sort of vibration and a slight change in RPM up and down.

This usually happens when the transmission is cold and when they do fail entirely, you will get a fault code for the torque converter not locking up.

Later torque converters have a revised seal design that solves the problem but the only real fix is to get the torque converter replaced or rebuilt.

Mine has done this for 20k miles without getting better/worse and no codes so I just take it easy until the car warms up. Some day I expect it will need fixed, but who knows when.