1996 Nautique starts but wont idle need help

[jammvonk]

My 1996 Ski Nautique with GT40 EFI engine starts but won't idle. This came on suddenly - one day everything was fine - next day it won't stay started. It will start and run if I advance the throttle with the transmission disengaged but when doing that it will drop the RPM every so often without my changing the throttle position. If I run it and move the throttle to idle it stall immediately but sometimes, after running it a while it may idel for 30 seconds or so.

After reading all I could in these forums I have checked and eliminated/replaced the following:

New ignition switch, it was a little quirky.
New ignition push button breaker, it too was a bit quirky.
Jumped out the safety lanyard.
Replaced the fuel pump relays (cheap and easy)
New spark plugs (ti was time anyway)

Based on other posts I have read I am thinking it could be a bad Idle air controller or Throttle Position Sensor. Any suggestions on what I should try next short of towing it 3 miles to a boat launch and trailering it to a dealer.

[NautiqueJeff]

Moving this to the Maint/Tech section.

[Jonny Quest]

Several possibilities to explore:

Idle Air Control Valve (IAC)
Throttle Position Sensor (TPS)
Manifold Absolute Pressure Sensor (MAP)

After that:
Bad fuel injector(s)
Fuel pressure at the rail (you need a fuel pressure gauge at the Schrader valve)
Fuel pressure regulator
High pressure pump in FCC (and the short rubber hose that develops cracks)

Not difficult to change out all of the above items for new. Common hand tools and a couple of hours free-time.

(Can't remember if a1996 has the FCC...)

[Tom_H]

I'd start with cleaning out the IAC passage with some carb cleaner. If it's gunked up, the pintle on the valve may not be able to open and/or let enough air come through when the butterflies are closed. Then I'd look at the valve itself and see if it's actuating. When you go key on, it should cycle to it's start position.

[JayG80]

How old are cap and rotor? Pull them to inspect and look at the Distributor PIP to see if it is ok.

not related, but keep an eye on the wire that passes thru the top of the FCC. The sealant breaks down and allows for fuel to leak. pCM has a retrofit kit to fix it.

[jammvonk]

Thanks everyone for the feedback. After many delays due to work, weather and other things I got time to work on it this week. After removing and cleaning the IAC things improved dramatically - the engine would idle after a short warm up and I was able to keep it running long enough to get it into gear and get moving. Then I replaced the TPS and everything started working perfectly. Thanks for the help on this one - had me wondering. My guess is that the TPS is actually what failed but the IAC contamination just made matters worse and after a hard week of skiing, tubing and boarding it was finally too much.