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OK, so I have posted about my buddy's '04 Monsoon a few times, but it is time to start a new thread and figure it out. We went skiing last weekend and I told him that this is officially a "thing" to me now, and I want to fix it. About five years ago, I noticed that his engine acted like it had a neutral disconnect that would break the ignition momentarily when you pulled it out of gear. The engine would hesitate for just a fraction of a second and then have a tiny surge afterward. Well, it is much worse these days, and doesn't idle very well. Any change of load at idle causes a fairly large surge, up to maybe 1000 or 1200 RPM. This has become quite a nuisance when using the boat, since the idle is so unreliable that you can't take slack out of a ski line by bumping it in and out of gear, and approaching the dock gives everyone a sense of impending doom. With that said, there's a catch: it only does this if you let the engine warm up and then restart it. That's right, you can start the engine cold and run it all day and it will run perfectly the whole time as long as you never turn it off. If you start it warm, maybe one out of ten or so will work correctly. This has been verified several times over several days of several hours of skiing. He has taken the boat to three different shops (including his original dealer a few hours away), and they all do something and say it is good (he just recently discovered the cold start thing, so they probably saw it working right too). At this point, all of the stuff you will tell me to do first has already been done at least once. I told him that if he will bring the boat closer to my house (it stays about an hour away during the summer), we can start swapping parts with my engine to see when the problem moves. We have different ECMs, but most of the other stuff should change OK. I won't make a list of what *has* been done, but here are a few things I can think of that haven't: - Clean connectors at the ECM. Well, I haven't done it. I did find a pushed ground pin on the MAP sensor. - Clean and check all of the other connectors. I spread the pins on the Cannon plug this weekend, but no change at all. - Swap out the ECM temperature sender. I checked the connector, but the sender is under the cooling hose and the plenum, so it is really hard to access. - Remove the distributor and check for bad bearings. He told me that one guy did this, but I think he only checked under the cap (and replaced the module, cap, and rotor). - Remove the throttle body and check for an obstruction. I cleaned it in place, and I have diddled the idle set screw, which does lessen the symptoms a little. Fuel pressure is OK. I removed the plenum and looked under it to make sure that a mud dauber nest hadn't gotten ingested or something. Another guy removed the plenum to carve a slot to get his fuel gauge on it (stupid design). So I'll stop here, but the thing to focus on is that it runs fine all day if you don't turn it off after a cold start. That keeps saying temperature sender to me because I can't think of what else the ECM cares about from turn on to turn on.... I need to get a MEFI data reader going for this motor. Any thoughts? P.S. After typing all of this, I can see where the MAP sensor could be getting hot and not working right. Manifold pressure is measured at key on, and is probably more critical for idle than any other operating range. I think one guy changed it, because I found the pushed pin on the connector and it looks pretty new. Hmmmm.