Replacing the IAC sensor (idle air control)

Not sure if this is the problem, but a boat mechanic told me that it probably was. I have a Merc 350 in my Centurion. It starts when cold, but after warmed up, I have to put it in neutral and give a little throttle in order for it to start. Also the idle is a bit low. Can I change this part myself? I have pretty good mechanic skills. Has anyone had this same problem? Or do you think it might be something else?

Its an easy swap. Did anyone pull diagnostic codes from computer with a scan tool?

IAC's are real easy to change. Its right by the throttle body. 2 screws and a wire harness connection. If its only having the issue running at idle but it performs awesome when the throttle is given, its probably the IAC. If it runs weird all over the place it could be the throttle position sensor (TPS). You could also have a fuel pressure problem too. If you don't want to guess any boat dealer can hook into that computer and find out if there are any fault codes which will tell you what needs to be replaced. The Merc multi-port EFI is more complex then an Indmar.

If you just have a TBI system, theres only a IAC and TPS on the throttle body, and coolant temp sender in the block. I don't think merc put a 02 sensor on the TBI units. The fuel pressure regulator is built into the TBI body. Its just a spring so theres no messing with it unless you are rebuilding the unit. All the parts needed for TBI can be purchased at an auto part store.

No codes taken, they want 100 bucks to hook up to it. It runs great while running just won't start turn key after its warm. But starts right up 1st start of the day. My dealer already changed out the TPS last year, but labor cost me a buck fifty. I think I'm gonna change it on his advice, thanks guys!

The engine is a 350 mpi 315hp tow sports. What is TBI?

TBI= Throttle Body Injection MPI= Multi Port Injection

They are mutually exclusive styles of fuel injection. TBI usually has fewer injectors and they squirt into the throttle body. MPI has an injector in each runner of the intake manifold, one for each cylinder.