# 90 Yamaha F90 TRL stalling immediately after starting. RESOLVED



## iMacattack (Dec 11, 2006)

Sorry for spelling mistakes above. Typing this on my phone without my dang reading glasses.


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## DuckNut (Apr 3, 2009)

this is a job for @JC Designs


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## Finsleft258 (Oct 7, 2018)

What year is it? It looks like it's the injected one.


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## Finsleft258 (Oct 7, 2018)

you can unplug the IAC valve and eliminate/diagnose that problem but your issue isn't how that typically manifests. Do you have a water separator?


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## JC Designs (Apr 5, 2020)

Call me tomorrow Capt!


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## iMacattack (Dec 11, 2006)

It’s an 05. Yes I have a water separator with a glass bowl. Will be inspecting them today 
JC call you later this afternoon. Thanks.


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## iMacattack (Dec 11, 2006)

@JC Designs I sent you a message.

I checked the fuel filters and they are clean. I pulled the plug on the IAC and tried to start it. No love. Same symptoms. I plugged the IAC back in. But I pulled the plug on the TPS and I was able to start the engine. Idle was very low. About 500 rpm but it did start. So may not be the IAC. When I shut down the engine I can hear the IAC cycling. It sound like a rattle.


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## JC Designs (Apr 5, 2020)

I’ll call you early this evening Capt. Gotta drive a long board today on a CF plug!


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## iMacattack (Dec 11, 2006)

Small update and a BIG shout out to @JC Designs .

In-between everything going on in his life James was kind enough to carve out a small chunk of time to listen to my YamaStall whoas and provide a bit of guidance. 

We discussed several possibilities but agreed it best to start with a stepped approach. One thing at a time. First order of business remove the IAC Valve and give it a good cleaning. As you can see from the pictures it was gunky. (is that a word?)


























I reassembled the IAC and installed it back on the engine. SUCCESS!!! It fired right up and purred like a kitten. So I let the engine idle for a bit to warm up. Figured no test is complete if the outcome can't be repeated so I shut it off after several minutes and fired it back up again. This time it was a bit more labored in starting and the RMP dropped by about 100 RPM down to 600 RPM. Hum... this is not promising. I revved the engine up to about 1500 RPM and brought it back and the engine stumbled a little. So I shut it down and tried to fire it back up again. No joy. Now it would not re-fire.

Did a little more testing but the results were the same.

James and I spoke later in the evening and we both have come to a common conclusion. The gunkieness (that can't be a word) of the IAC may be part of the issue. The other part is probably the stepper motor in the IAC is going bad due to either worn condition or contamination. Net result, replace said part.

Jumped on boats.net yesterday and ordered a new IAC. Should be here in a couple days.

In the meantime I'm going to fully disassemble (i.e. destructive disassembly) the old IAC to see how it works and see if I can find the root cause. I'll post the results when I have them.

Once the new IAC arrives I'll install it and retest.

Thanks again for all your help @JC Designs !

Cheers


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## JC Designs (Apr 5, 2020)

iMacattack said:


> Small update and a BIG shout out to @JC Designs .
> 
> In-between everything going on in his life James was kind enough to carve out a small chunk of time to listen to my YamaStall whoas and provide a bit of guidance.
> 
> ...


Always happy to help Capt!


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## iMacattack (Dec 11, 2006)

Follow up #2.






She's ALIVE!!!

First and foremost a huge thank you again to @JC Designs for helping me diagnose the issue and saving me a ton of money!

I took the old IAC apart and over all it didn't look "bad" but there was corrosion on the main pin of the stepper motor. New part I ordered from boats.net also pictures.


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## m32825 (Jun 29, 2018)

Thanks for sharing with the rest of us so we can learn. I hate threads that stop before you hear the rest of the story!


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