How can I do a reset on the TPS on a merc 350? Pulled the boat out of storage, dropped it in water, took it for a quick spin throttle wouldn't come back down fully -- high idle, took it back out and came back throttle is even higher now. Sounds like the TPS to me or is there something else that could be making it hold high throttle position when the cable is in neutral?

I know of two ways to do it on the GM trucks...not sure if its the same thing for boats but here they are:

with key key off.
Unplug TPS.
Turn key on for 5 seconds.
turn key off.
Plug in TPS.
Turn key on.
Closed throttle should show 0%. on scan tool


for the newer drive by wire systems:
start and let engine idle for 3-min
turn engine off for 60 sec
start and idle again for 3min
and that's it.

You don't need to reset the TPS. You have a vacuum leak causing the high idle.

Do you mean to clear a TPS fault code that is stored in a marine ECM app ?

There is no reset nor even a reset using the scan tool

So what year and ecm do you have here ?

How about checking the throttle plate operation and closing

also the throttle cable for its movement or lack of ? Unhook it and what happens to the idle ??

ALso agree about a vacuum leak and those are easy to find with a small propane hand held tank.

how clean is flame arrestor ?

PCV operation and that valve ? I just had an indmar and the wrong PCV valve was install by the owner. It idled at 1000 to 1100 - changed it and all good. after that. Even lake tested it. ..

Every time I've seen a high idle with this motor it has been a vacuum leak. I have NEVER had to reset a TPS on this motor. Could be a disconnected line, cracked line etc.

I have seen corrosion on the throttle plates and shafts causing higher than spec idle rpms

bad throttle cables as well

PCV operation as I mentioned and or the PCV hose off at the throttle body can cause high idle.

Bad TPS

and of course a vacuum leak

and also what set up 350 is this ? MEFI 1 or 2 or 3 or 555

if its a 555 the IAC and or the IAC system can cause Idle issues. Important info missing from his post