Merc 575 SCI fast idle (too fast)...
 

I've got a single 575 in my 03 Pantera, 40 hrs when I bought the boat, 84 now. Just last night, it started having an intermitent fast idle problem.

I know first hand that when you first start the engine it idles 300 ish fast then settles right down to 800. What's new is that when I come off plane it will stay idling at 1100 in gear and higher out of gear, as much as 2800. If I kill it and restart it goes back to normal idle speed. I've checked the throttle linkage etc, all seems to be in order and returning to closed throttle position etc so I'm inclined to think I've either got a vacuum leak or a IAC solenoid with a split personality- any other ideas??

I plan to get a scan tool on it in the next few days but hought I'd see if anyone had a clue??

Re: Merc 575 SCI fast idle (too fast)...
 

Scan that thing. Your TPS (throttle position sensor) could be a culprit. If your IAC was sticking open I don't think It would idle so fast (2000 rpm above normal sometimes) Also, if the IAC was having a problem you might have some intermittant stalling problems when you abruptly cut the throttle. It does also sound like the vacuum could be screwed up. I hate these kind of problems. Makes it real hard to use around the docks sometime!