I have issue with my XKR (x150) where the rpm fluctuate dramatically as the idle stabilizes at cold start especially in the morning. As the rpm trying to settled down with the needle pointer between 1000 to 2000 rpm. I can feel vibration from the body it seems like the engine is going to shut off like a feeling of detonation. RPM will stabilize in a few seconds and slight vibration will be there. No trouble code registered, no misfire data, no engine light, all engine and transmission mountings are OK. cat converters and sensors are all new. The car mileage is 41k miles.
Are these normal condition? I recently bought this car.

Please advice if you have encountered same issue. Thanks

 

It is probably still running open loop and cannot figure what code(s) to flag.

It doesn't sound normal.

When running happily, do the usual fuel trim tests in case you get clues.