Idle running fast gt-40

[JSchimpke]

I have a 97 Nautique with the GT40 motor: it idles fine when cold but after it is warm and after running under load ( pulling a skier), it idles too fast (1200-1500) when you drop it in neutral. I have replaced the air intake module behind the throttle body with no improvement. I have also lubricated the throttle linkage. Any suggestions?

[Peter6000]

I have a 97 Nautique with the GT40 motor: it idles fine when cold but after it is warm and after running under load ( pulling a skier), it idles too fast (1200-1500) when you drop it in neutral. I have replaced the air intake module behind the throttle body with no improvement. I have also lubricated the throttle linkage. Any suggestions?

Pull the plug on the idle air control valve when rpm high rpm should drop below 600 and almost drop out.
If rpm stay up make sure the throttle valve codes all the way.
You can try cleaning the idle air control valve.
You can also take it off plug it in, when you turn on ignition you can see the piston moving should be open when turning on ign.

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[JSchimpke]

I pulled the plug on the IAC and the idle dropped down to normal, plugged it back in and it jumped back up to about 1400. What does that mean? Is the piston hanging up? ( I just replaced the IAC last season).

[Peter6000]

I pulled the plug on the IAC and the idle dropped down to normal, plugged it back in and it jumped back up to about 1400. What does that mean? Is the piston hanging up? ( I just replaced the IAC last season).

It should not go to normal it should almost starve or even die something like dropping down to 300 rpm,
I have a feeling your throttle does not go all the way to close position.
Remove the throttle cable and perfect pass on the throttle body.
If it still runs more than 600 rpm with the idle air valve disconnected try to use the adjustment screw to bring it down.
Also check you vacuum hoses make sure they connected and do not leak.


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[JSchimpke]

I checked the throttle linkage and at neutral, the throttle body plate was slightly open so I adjusted it so it closed. I ran the boat once and so far it is idling normal. I'll keep my fingers crossed! Thanks Peter for your advice.

[Peter6000]

I checked the throttle linkage and at neutral, the throttle body plate was slightly open so I adjusted it so it closed. I ran the boat once and so far it is idling normal. I'll keep my fingers crossed! Thanks Peter for your advice.

If I remember this right maul says to disconnect iac valve on running engine and adjust throttle blade to almost kill the engine. Then plug back in.

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[SGaetz]

Adjusting the idle does not do anything in my 1997 gt 40 as the system takes over and brings the idle back to baseline.

[Peter6000]

Adjusting the idle does not do anything in my 1997 gt 40 as the system takes over and brings the idle back to baseline.

That's what it is suppose to do, to test and adjust you pull the cable from the idle air control valve. The walve closes and idle should drop way down, engine almost dies.

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[SGaetz]

Fair enough. I suppose that I can deal with the high idle. The real issue is when starting, hot or cold, the idle takes ~15 seconds to settle. As well, at the end of a pass when dropping the skier, again, ~15 seconds to settle. I replaced the IAC and temperature sensor but growing weary of throwing parts at it.

[Peter6000]

Fair enough. I suppose that I can deal with the high idle. The real issue is when starting, hot or cold, the idle takes ~15 seconds to settle. As well, at the end of a pass when dropping the skier, again, ~15 seconds to settle. I replaced the IAC and temperature sensor but growing weary of throwing parts at it.

Test all sensors the values are in the proBoss service manual. The map puts out frequency all the others you can use a voltmeter.
I would start with the TPS.
Also check for vaccum leak.

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[SGaetz]

My issue may be a faulty ground in the IAC as the boat ran fine with it disconnected. Does anyone have a wiring diagram that I could refer to?