I have recently bought a 1998 Ski Nautique TSC1 with a PCM GT-40 engine.

Unfortunately the engine is giving me a little bit of trouble. After start up the engine surges for 2-3 seconds at around 600-800 rpm and then immediately goes up to 1800 rpm, it will stay there for 5-8 minutes and then slowly settle down to 800 rpm. After those 5-8 minutes of higher rpm it will settle and then sometimes go back up to 1800 rpm for a few seconds but eventually after that stay at 800 rpm.

Other than that the boat runs great and has good power. When you are docking and putting it in and out of gear you can notice that when taking it out of gear the rpms will raise shortly to about 1200 and then fall back down to about 800 rpm.

It doesn't matter if the engine is cold or warm, it will always go up with the rpm for a few minutes after start up which is quite annoying.

The previous owner has already renewed the injectors, the ignition distributor, the spark plug cables, fuel control cell (used one though), and the IAC Throttle Air Bypass.

I will clean the mesh filter behind the IAC next time I am at the boat and check if it does change something if I unplug the IAC.

Any other ideas what to look out for or what could cause the problem? Maybe a bad ECM?

Thanks!