2008 DF200 not returning to idle.

[vroomZOOM]

Hi there. I have an annoying issue. Motor start up and idles just fine. revs up and gets on plane perfect, WOT is good. Now when I pull back to idle, it will not return to idle but stays at 2000 revs. If I turn the engine off and restart it idles normally. Any ideas?

[frogbite]

Maybe a faulty IAC (Idle Air Control) valve? The only other things I could think of an not sure if they would apply would be crank position sensor or a TPS (throttle position sensor)

[vroomZOOM]

How do I test the CPS? I plugged in and the tps seems to be working just fine. Dunno about the IAC, because if that failed then it would not maintain rpms when put in gear, or not run a little faster at warmup then slow down? Checked through my computer and the IAC is working OK.

[frogbite]

Not sure, never have had to test it myself. Like the IAC and TPS, I know it can throw faults that should be stored and viewable in SDS. When I have had IAC failures it is typically stuck in the fully extended position. Not sure what would happen if it were only partially extended or not extending at all. Is this a single engine boat? If you had twins I would suggest swapping some parts one at a time. Including the ECU. Other than that, I am at a loss as I have never experienced this so have given it a lot of thought.

Hope you figure it out though, it is an interesting/annoying problem.

[vroomZOOM]

There are no fault codes, and the engine sounds and runs absolutely perfect other that it doesn't want to slow down. I can see the IAC duty cycle in sds and I can see it is constantly adjusting. I will try adjusting the throttle cable, maybe the throttle is not returning to fully closed?

[frogbite]

If that were the issue, then why does shutting it down and restart it correct the idle issue?

[vroomZOOM]

well now I am really stumped....

[redlowrey]

There are no fault codes, and the engine sounds and runs absolutely perfect other that it doesn't want to slow down. I can see the IAC duty cycle in sds and I can see it is constantly adjusting. I will try adjusting the throttle cable, maybe the throttle is not returning to fully closed?

SDS data is only good for people that can understand what it means, for instance if the iac valve was keeping the rpm high it would have been around 90% duty cycle, if the high rpm was caused by an air leak or the cable, the ecu will be trying to drop the idle by closing the pintle and the duty cycle would be around 0 )%, If the throttle position signal voltage is to low the ecu will increase duty cycle, if coolant temp sensor voltage is too high the ecu will increase duty cycle on the iac valve.

These are only a few examples of what a tech would look at on the sds and get a picture of what is going on straight away, and the examples will not log a code. When you turn the key on the ecu will look at throttle position, map sensor voltage, temp sensor voltage to determine how much duty cycle and injector pulse width it will apply to the injectors and to the iac valve for a stable idle when cold.
It sounds like the iac valve is the problem, but it might be commanded to to do that from wrong information from other inputs.

Do a simple test remove the plug and run the engine you will soon find out if it is the iac valve or your cable. Note the temp sensor voltage, exhaust temp voltage, and the duty cycle on the iac valve when runing at high rpm and come back with your results.

[vroomZOOM]

ok, thank you, that will give me a start. Took me a little to click but your test makes sense, I will try that. Should I just start it up and then unplug once it warms up so it stays running? When I go out next time I will grab my computer and do a data log with the parameters you asked for and upload it. I am more inclined to think that it is not the iac, but rather that it is getting the wrong inputs, but will have to test to make sure. I am new to these computer controlled engines, always dealt with carbs up to now, so it is a bit of a learning curve right now

[vroomZOOM]

alright, here is a run log with a bunch of parameters. at the end of the run, I returned to idle but it would not idle. TPS data seems to be off

https://drive.google.com/file/d/1BZ8...ew?usp=sharing

[redlowrey]

It looks like Your engine has been running entirely off the iac valve, 1219 rpm, duty 80%,No Throttle angle no data. The computer is not seeing any throttle angle so it increased the duty to 80% and staying there. Have you touched the throttle plate adjustment. Looking at the throttle angles they are all over the place.

When the engine leaves the factory the base idle is set on the throttle plate at around 500 rpm, just enough throttle opening so the engine can idle on it's own with out help from the iac valve, so under normal circumstances when you turn the key on the computer will see a curtain throttle angle, and a throttle position signal voltage under 1 volt, when you turn the key to start duty will go to 80% depending on engine temp and when running will drop the duty as the engine warms.
I think you better check the operation of the throttle position sensor and clean the under side of your throttle plate and housing with carbi cleaner.

[redlowrey]

I don't mean the engine operation from the iac valve, I mean the idle control side of the valve at start up, not opening the throttle with the cable.

[vroomZOOM]

I will check the tps, maybe it is loose? at the beginning, the engine starts up, and then settles down to an idle of 688 rpm, with a valve duty of around 33%, TPS showing 0 degrees, this is how it should be. Near the end, I close the throttle fully, but TPS is showing around 3 degrees, and engine speed is 1875 rpm. If I restart the engine then TPS reading goes to 0, and idle is normal! How the heck is that happening?????. Any way to test the TPS? Still, maybe after the engine shuts off, there is no vacuumpulling on the throttle plates and then they close fully after shutdown? But yes, the TPS data seems pretty jumpy so it might be on its way out.

Secondly, Could someone describe how to adjust the throttle cable? As you can see the throttle only ever reached a maximum of 70 degrees, I might not be getting good WOT rpms!

[redlowrey]

For your iac valve to function properly the information from the throttle position signal voltage has to be spot on other wise the computer will not know how much duty to keep on the iac valve. Your computer must receiving some information from it other wise the check engine light would have come on.

If you have not touched the throttle plate adjusting screw, the throttle plate adjustment should be ok, you will never see 100 degrees of throttle opening, the computer needs to see between .7 volts at closed throttle and around 3.8 volts wide open throttle on the yellow wire on the tps key on, when you are doing this test tap the sensor and see if the voltage changes indicating it is faulty.

You need to get this right before you do a base idle adjustment with the air bypass screw.

[redlowrey]

I was just reading your post again what do you mean vacuum pulling the throttle plates closed when you switch off, the throttle plates should not be able to move unless you open the throttle by the cables they should be closed against the factory setting of the screws stops.