TSIO 360 EB running lean at 12000

Hi all,
Yesterday I was flying on a Seneca II equipped with TSIO 360EB Teledyne
Continental engines.
The first flight (Dusseldorf-Milan) took 2 hours, FL 140, everything
working perfectly adn according to the manual.
The second flight (Milan-Rome) had the following inconvenience on BOTH
engines:
At FL 130 29" MAP 2400rpm the indicated fuel flow was 12 Gal/Hours
but the Mixture control lever were in the "Full Rich" position.
I could not move them to lean mixture since the fuel flow was going
down to less than 12. The speed was correct (about 170 KTAS), and the
engines were both a little bit too hot, but not that much.
I repeat it was behaving like this for BOTH engines. And this
sound strange and new to me..

I still have to fly again with the same plane, and it will be checked
by a specialist before, but, is there anybody who has an idea about
what was happening ?

Silvio