I've been searching the forum with a very basic question but haven't found an answer so far, could someone assist please ?

The background is as follows. Late 90's 502 MPI. The last time I ran the boat all started well, operation as normal. I anchored for a while and when I went to restart the engine it took a lot more cranking than ever before, wouldn't hold idle, missed and died. It would idle by advancing the throttle a little, but tended to hunt, and would only hold steady at about 900 rpm.

The engine appeared to run fine once on the move, but back at the dock the same problem manifested itself. I stopped and started the engine a few times, let it cool, same problem.

Reading through the forum I'm wondering if the IAC has failed ?

So after all that, my dumb question; I have the IAC in my hand and even exerting quite a lot of pressure the pintle doesn't move. I understand it's a worm drive to a stepper motor, so it doesn't move easily, so how much pressure should it take ?

The boating budget this year is very slim, so I'd like to address this myself if at all possible. I'm hoping a new IAC will solve my woes, but may well be deluding myself.

Thanks for any feedback

one thing u can do ,is see how the engine runs after a cold start,,if it runs good when cold,,,but is hard to restart after running a while,,i would do a search about vapor lock

Thanks, but I think it may be something a little different to that. The boat has run solidly for 5 years without missing a beat. Nothing has changed until this problem showed up on an otherwise boating as normal day. Once above idle it was running fine. Whatever's gone wrong happened between one shutdown and the next startup. No little hints over time.

Plug iac in with it out , start motor for a second and it should extend, thread it back in and install it IF it does move, if it doesn't replace it. I remember they thread in and out when off if you want to move the pintle but that doesn't mean the motor is working, Smitty

Ah, great suggestion, thanks. One thing, right now it looks as though it's extended, should you be able to push it back in to the IAC body using hand pressure ? I can't get it to move at all right now.

i don't think it moves except by turning the worm gear.

Just a thought here but the Baja I sold last fall suffered the same problem after running great for two seasons. Ended up being a vacuum leak, mine did have a side mount whipple on the 502 but it acted exactley as you described except I had to keep mine about 1000 rpm to keep in running. Even without the whipple i would check for a vacuum leak. Guy that bought the boat pulled the whipple and found several leaks and after the repair it idled steady at 600 rpm.

if iac checks out ok i would also check for carbon build up on back of throttle plate or for a possible vacuum leak.

sorry 2 repeat bigred, shud of read all of the posts..but i also had same problem as him.

10-4, I've cleaned the throttle body.

On a car I'd check for a vacuum leak by spraying brake cleaner around the joints and checking for a change in idle. Can I assume that's an appropriate approach here ?