I have two X300s
a 3.2, and an XJR6 with Andy’s EPROMs and a Powerhouse 110% supercharger drive pulley.

The 3.2 is running perfectly, hardy gets used, but the LTFTs have been sneaking up and are at 45%. All the sensor readings on my OBDII reader are normal, the O2 sensors cycling normally on the voltages. So I’m puzzled, and It’s running like a dream.

also, the XJR has always had LTFTs of about 10.9% for ages - 2 years.
then the battery was disconnected at the mechanic’s for about 10 days while the front shocks were away being rebuilt and new front V block mounts were fitted. Once I got it back the LTFTs dropped down to 1.2%, then 0.0%, and I thought ‘perfect’.
Today they are at -0.8%. It is going better than ever, I don’t know how to interpret this....

 

As it worked so well on the XJR why not try disconnecting the battery on the 3.2!

I would guess there is an air leak on the 3.2, might be worth checking around the intake and maybe the breather.