I have a idling issue on my LS2 supercharged boat engine. It has a mechanical throttle body with intergrated IAC and TPS. It is a 2bar SD tune. When I start up, kold or hot engine, it idle perfect. Idle is set to 750rpm. The TPS shows 0%. After running 4-5000rpm for some time, it will idle at 1200rpm and TPS shows 7%. All mechanical is ok, and throttle blad is closed in same position as it is when TPS shows 0%.
If I turn of ignition for 10 sec, and then back on, TPS will return to 0%, and idling is OK.

Can anyone give me some hints?