2006 Volvo 8.1 GI. Throttle Problem.

2006 Carver 390 w twin Volvo 8.1 Gi engines. MPI engines w about 400 hours. Went to run boat last week and had an issue with port engine. Both engines started and idled fine. Left slip with no issues. When I went to accelerate the port engine would not increase in rpms at all. Returned to dock and checked throttle linkage which connects to the throttle position sensor. Connection was fine. Checked all connections I could see including tps and all appeared fine. Next morning started boat and it would idle up, shut it off and immediately restarted and it wouldn’t go above idle again. It always restarts and idles fine but will not increase rpm’s. So I replaced the tps and it started and ran the first time correctly then on second start nothing above idle. Next I verified the old part was good and it’s not the tps. So $351 later I’m no closer to a solution and feel foolish throwing parts at it. Any help most appreciated. And to be clear the TPS is mounted near the top of the block and connects electrically to the engine. There is no mechanical function of the tps it’s all electronic…I.e.. the throttle cable connects to it and that’s it.