My port engine shuts down to 2000 rpm after powering up following trolling or idling through no wake zones. It will not exceed 2000 rpm’s until shut down and restarted several times. I had the cam sensor replaced, but that did not solve the problem. I have heard that the anti-siphon valve, which is spring loaded, might be to blame. This is a 2005 boat and engines, with about 1480 hours. Until now, the engines have performed flawlessly. They have been well cared for and serviced. I appreciate any ideas about how to solve this problem.