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TPS or IAC


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I'm planning on replacing both, but I'm curious if anyone thinks my symptoms point to one or the other. The boat always starts up and runs fine, the issue arises when returning to idle from a higher speed the idle creeps up to 16-1800 RPM and stays there once I'm in neutral. I used to get some stalling before I cleaned the throttle body etc, but now it is just a high idle after coming off plane. I'm leaning toward the issue being the TPS since it idles fine on startup every time.

Thanks,

Daniel

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I'm not sure, but it may be interesting to try one, then the other, to determine which is the culprit. A lot of owners have the same issue. Thanks in advance for following up and letting us know the results.

Steve B.

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2 hours ago, Steve B. said:

I'm not sure, but it may be interesting to try one, then the other, to determine which is the culprit. A lot of owners have the same issue. Thanks in advance for following up and letting us know the results.

Steve B.

I've thought about that, the problem is that still requires buying both :Tease3:... oh well, I guess I'll know soon enough.

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5 hours ago, dfarhood said:

I'm planning on replacing both, but I'm curious if anyone thinks my symptoms point to one or the other. The boat always starts up and runs fine, the issue arises when returning to idle from a higher speed the idle creeps up to 16-1800 RPM and stays there once I'm in neutral. I used to get some stalling before I cleaned the throttle body etc, but now it is just a high idle after coming off plane. I'm leaning toward the issue being the TPS since it idles fine on startup every time.

Thanks,

Daniel

I had problems getting the boat to start and idle, replacing the IAC fixed it. Seems like you have a different problem. 

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So I swapped the TPS this morning and it ran worse then with the original. I thought I had read here in the past that it learns the throttle range on its own. Is there a start up sequence that I need to do? The idle just kept climbing up to around 3000 RPM with  the new TPS. I swapped the old one back so I could ride this morning but I'd like for the engine to actually return to idle when in neutral...

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1 hour ago, MadMan said:

I would replace the IAC.  You don't want to be putting the trans in gear with the engine at 2000 rpm.

I'm aware doing that is bad for the trans. My understanding though is that the IAC is there to prevent stalling and not reduce the throttle. With the old TPS and IAC I can idle all day after start up in and out of gear at a no wake speed. Once coming off plane from a higher speed the idle will usually be up in the 16-1800RPM range and if bumped in/out of gear it will drop to 1100RPM (again I know this is not a good thing to do to the trans).

This morning with the old IAC but the new TPS as I was trying to idle out of the no wake zone the engine gradually climbed to 3000RPM. I thought I had read somewhere about the TPS/ECU needing to learn the new respective settings for WOT and idle so I quickly did a WOT run to the other end of the lake. After coming off plane the engine was still at 3000RPM in neutral so I anchored and swapped the old TPS back in since those characteristics were more desirable then the new ones.

I did buy a new IAC but from the way it is acting I'm not really understanding how that could be the culprit. I was hoping to install the TPS have it work and return the IAC. I guess I'll try the other two combinations tomorrow but the symptoms don't really align with my understanding of what the IAC does.

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The TPS only senses the position of the throttle, it does not change the throttle position.  The IAC is sort of a "mini-throttle" that adjusts the amount of air entering the engine to control the idle speed.

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That is exactly how I understood it. What I don't get is why with the throttle in the same position (butterfly closed) after start up two different TPS are causing such different behavior. It seems to me that they should both see the same position, send the same signal and the IAC should react the same way, or not at all if it is not functional. Clearly if I'm leaving the throttle in the same position and the idle is different with the different with the different TPSs the IAC is changing positions as nothing else on the throttle body is changing to cause a different idle.

I guess what you are suggesting is the IAC is not responding to the ECU correctly regardless of what the TPS is telling it? This all seems possible to me, but something about the TPS creating such havoc really bothers me and I'd like to understand why it is doing that.

Anyway my plan for tomorrow is to try the new IAC with the old TPS first to see how that works out and then try both the new IAC and TPS.

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A couple years a ago I had 2 sensors (oil pressure & TPS) fail on my boat the same week.  Because of this, I replaced all the sensors (from the local auto parts store & ebay).  No problems since then.

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So new IAC with old TPS the idle started around 2000 RPM and gradually dropped to 1100 RPM. New TPS and new IAC idle started at 2000 RPM and never dropped. Again running both the old parts is still better functioning, any other ideas?

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On ‎6‎/‎19‎/‎2016 at 10:53 AM, dfarhood said:

So new IAC with old TPS the idle started around 2000 RPM and gradually dropped to 1100 RPM. New TPS and new IAC idle started at 2000 RPM and never dropped. Again running both the old parts is still better functioning, any other ideas?

Have you checked to see if the engine controller has set any DTC's?

 

You can also unplug the TPS, start an run the engine for a couple minutes, then verify DTC 22 is set.

Edited by MadMan
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On 6/22/2016 at 8:33 PM, MadMan said:

Have you checked to see if the engine controller has set any DTC's?

 

You can also unplug the TPS, start an run the engine for a couple minutes, then verify DTC 22 is set.

No I have not. I guess I need to buy or borrow a codes scanner?

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