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My 2008 F90 idles too high when it gets all the way up to operating temp. It almost never does it in the first ten minutes of use. It nearly always does it when it's been running hard for ten minutes. Often turning it off and restarting it will fix the problem. Usually I have to do that several times. Also, after letting it run at that high idle (usually 1800RPMS), it will then idle down--it seems like too far, and run really rough for 1-2 minutes, and then often just shut down--its seems like it shuts down because it is running so rough. But if I restart it it will often be OK, though there is no telling where it will decide to idle then--might be too low at 500 or might be 1400. I cleaned the throttle body, which wasn't really very dirty. Engine has 150-160 hours and is up to date on maintenance. Good fuel. No issues ever before. This has been going on for a month.
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Are you familiar with the idle air control valve? Find the connector that attaches to the valve. Carefully inspect the wires to the terminals within the connector for any signs of distress. It is a known issue that when removing and replacing the cowling that the wires can get damaged. If and when they do they will cause all sorts of mayhem in the form of erratic engine RPM's. -
IAC valve
Good thought. and thanks for the response. I'm pretty sure the IAC valve is the thing screwed onto the top of the throttle body, right? it looks like it's a position sensor for the throttle, but maybe I'm wrong and the thing actually exerts some control on the valve in the throat of the throttle. I took it apart and cleaned it yesterday, though I was suspecting something like it was stuck or dirty. It wasn't very dirty when I got it apart. The connectors and wires looked fine, but I'm going to go outside and check it again right now and tell you what I think. I suspected that IAC valve was the problem, and would have just bought one and tried it (it looks like a $20 part), but when I looked it up, it was $280! So I'm trying to be more certain before I just go replacing parts.Originally posted by boscoe99 View Post
One thing I noticed when I had the throttle apart is that even at fairly high RPM (like 2000 but under no load) the valve inside the throat of the throttle is barely open to allow air to enter--it only opens about 1mm. Is that normal? It looks like it's supposed to open further than that, but maybe it wasn't opening any further because the engine wasn't under load.
I'll let you know about the wires/harness. Where on the wires does it usually get dinged?Comment
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Item 10 in this illustration. Not to be confused with the TPP (Throttle Position Potentiometer).
2006 and Later F90TLR_041 Yamaha Outboard INTAKE 1 Diagram and Parts
The wires can break internally (hard to find) or they may break at the interface of where they connect to the terminal. Look at the insulation for signs of any mechanical damage.
With no load on the motor it does not take much air at all for the motor to run at a high RPM.Comment
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AH, OK, I was looking at the wrong part, labelled here as the throttle sensor assembly. It looked fine. I'll go back and check the control valve assembly you referenced (item 10). Thanks for clarifying and sending the picture.
And thanks for the clarification on the air utilization question.Comment
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I checked the wires and connectors and pins to the IAC valve, and it all looks fine to me--in fact it all looks like new. I have not yet removed the valve itself from the intake, but I will do that today. (Couldn't lay hands on the bit last night). Is there anything specific I should look at or clean on the inside of the IAC?Comment
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Hi all,
My engine is 90hp 4stroke.. problem is the engine die out when i put it on idle.. any idea what will be the problem? If i revv up the speed, no problem and only when i put on to neutral or idle its die out...Comment
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