Problems With Indmar Engine

I have a 325 hp Indmar MPI engine in my boat. The engine starts fine and runs well under all conditions except one. Strangely enough, the boat chuggs and backfires for about half a minute after it sets for more than an hour after being run at normal operating temperature. You have to constantly pump the throttle the whole time it is chugging along to keep it running because it will not idle and just dies otherwise. Once you baby it through this little episode it runs fine again. You can shut off the boat for 10, 20, 30 or 45 minutes and it will start right back up with no problem. It starts up cold just fine too. I seems to only happen when it is still warm but has been sitting for more than an hour.

Has anyone else had this problem or know what might be causing it? It is sort of like vapor lock but I was under the impression that EFIs don't get vapor lock.

TPS (Throttle Position Sensor)maybe? the backfire is odd though?

I've heard of this problem, look on the supra web forum. I think lowdrag on this site was the one who brough it up, don't know what the final resolution was. I've heard that it may have been some bad gas or winter mix. Does sound like vapor lock. I think someone else said that if they ran their blower for a while after they stopped that it helped.

Could be something like a leaky injector, could be a faulty sensor, could be a...

It is only possible to throw ideas out without actually feeling how it runs when it is acting up. Take it to the dealer and have it scanned for codes.

try a fuel filter for what it costs it's been known to help.

I had a little spring cleaning done on the boat at the opening of the season which included new fuel filter, water separator, plugs, etc. Also at the time there were no error messages. I'm definitely going to have him look at it again. I was just hoping someone might have had the same experience and know how to fix it right off the bat.