Ok so I bought a 1996 crownline with a 454 mag from a friend. I know the boat but I don't know what's wrong. First the boat was left open to the weather and the boat filled with rain water. It got in the fuel tank and after it was drain it was attempted to start. There was enough water in the boat to be up to the engine. The engine had water in the oil which I assume came in from the intake and past the rings, water in the fuel rail and water in the outdrive from sitting filled up so long. Guy swears it ran great no problems until it filled up. I rebuilt the VST and purged as much of the water out of the fuel system as possible. New filters, new oil and new plugs. Boat fires up and runs but idles around 1200 to 1500 depending. When I first start it it runs around 1200 but after I rev it it idles around 1500 and wont settle down back to 1200. I let it run for about 15 minutes twice. I pulled all the plugs and number #8 has water on it. I start the boat with the plug out and let it expel any water twice but still get water on the plug. I dont know if there is more water in the fuel rail but I think one cylinder with water on it is doubtful especially after 15 minutes of runtime. So i feel i need to start looking for a busted head gasket or can a exhaust riser gasket cause this? If i do a leak down test how could i tell? Seems to me if its the head gasket it will leak down no matter what. If the exhaust riser can let water in then should not leak down on compression stroke but when the exhaust valve is open it will let water in? I still don't see water in the oil as of yet but the condensation on the plug doesnt say there is enough water from that cylinder to have any milky oil yet.

Any clue what is causing the engine to idle so high? I hear a ticking lifter but not a cause for high idle. TPS, idle air? What do I test first?

Did it freeze when it was full of water??

High idle is a vacuum leak on that motor. With the water intrusion you speak of I would estimate you have a host of problems starting at the keel and going to the top of the motor.

He told me it did not freeze. I mean anything should be considered possible but I know he winterized but all that water in the engine could have been a possibility. Supposedly the rain was after the freezing period.

As far as the leak how do I go about finding a vacuum leak in this engine? I need a diagram of the vacuum system I guess.

So I got to reading on vacuum problems and it made me wonder about something. I bypassed the fuel tank in the boat till I could clean it throughly so I have the fuel line stuck in a fuel can of gas. I can't imagine it but can this cause the high idle?

Is the temp guage working correctly? If the temp sender goes bad it can make the IAC come up some as if the engine were cold and at fast idle.

Hate to be the bearer of bad news but its FUBAR. Cheaper to find a good running one. Your electronics will fail totally as they are already starting to. If water sat in the motor, you probably have a stuck ring or rings. If you do manage to get it on plane, you sill spin a bearing and trash the rest of the motor. Find a 502 take out that is running and drop it in. When you go to sell the boat, Pull the motor and sell it someone else. and call the boat a loss. Trust me I, as well as everyone else on here have lost their fair share on boats. Just trying to save you some time and money.

Chris

I'm questioning the Friend part

1996 Crownline is full of wood every where - the floor all the stringers the transom all interior bases and so forth. You are on the way to rot. its already 23 years anyways old get rid of it. Prob had some rot before it filled up with water. Also it does have foam filled in some of the under floor cavities. I know Crownlines very well as my area was filled with them in the 1990 s.