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Discussion Starter #1
I have struggled with a rough idle when hot issue on my '05 wee for a while(2 months tinkering on weekends trying to pinpoint the cause). When it's all the way warmed up the idle will drop a few hundred RPMs. I think I have finally figured it out. My IAP output voltage goes nutty when the bike gets all the way warmed up and is at idle. When I take off from a stop under those conditions it sputters and tries to stall. It seems to be OK once the RPMs get above 3,000-3,500. The IAP sensor is crazy expensive (IMO) at $265 so I'm wondering if there is anyway to eliminate it entirely? If I disconnect the vacuum line the bike runs much better. I attached a marinade syringe with a vacuum line to the sensor and as soon as I apply a vacuum to it the idle goes way down and gets rough. I don't want to unplug the sensor because i get an F1 error on the display and I'm not sure how bad it might be for the engine if I cap off the vacuum line and leave it disconnected from the sensor.
 

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Welcome to the Forum. I think the reason that you haven't had a response to your question, is that like most members here, I don't know the answer. Is there not perhaps someone living nearby you, who has a similar model Wee and is prepared for you to do some comparison testing? My first thoughts would be a bad connector / wiring somewhere. There was a post of a vacuum leak Erratic idle and IAP Sensor, but this was not reported as eratic IAP voltage output. Perhaps check / confirm the charging voltage accross the battery.
 

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Discussion Starter #3
I have checked almost everything possible. The charging system is good. I did a continuity test on every wire from the ECM to the sensors and servos that they lead to and all the wiring is good. Input voltage on the IAP sensor stays constant while the output voltage is erratic. I am positive that I have an issue within the IAP sensor. I am hopeful that a replacement sensor will take care of the issue and was really just curious if there is a way to eliminate the sensor altogether without creating another problem. I have seen a lot of threads on here describing similar issues (none of them posted that a solution was found) so I am concerned that the sensor doesn't stand the test of time. At $265 I don't want to have to replace it every couple of years.
In searching for the root of my problem I found that the TPS was out of spec so that was replaced and adjusted. The secondary TPS was also out of spec and the secondary throttle valve servo was not operating properly so I sourced a used set of throttle bodies to remedy both. Throttle bodies were synced and STPS was adjusted. All vacuum lines were checked. The PAIR valves were checked and cleaned and the PAIR servo was tested. The ECT sensor and IAT sensors were both checked cold and hot. The CKPS was checked (although not for peak voltage because our local Suzuki dealership service center is a joke). One of the coils was showing some rust so I replaced both out of an abundance of caution. Spark plugs were replaced with iridium and then again with copper core at the suggestion of another wee owner. I also bought a used ECM (new no longer available for k5) and the problem persisted.
 

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Discussion Starter #5
I would have to research and see if i could find one that would work. The output voltage for k7+ was different than on the k5
 

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Should you find more info on the IAP, kindly post here. This has been a learning curve for me, as I haven't had any cause to delve this deep into the IAP. The major info that I have located on the IAP have been for the Vee. One of these threads discuss the IAP voltage pulsing under control of the ECU. IAP specs. Don't know if this link is going to be of any value to you. Good luck in finding a solution.
 

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Discussion Starter #7
after installing the used IAPS the bike is running a bit better but not entirely right. The weird thing is that with the old sensor if I applied a vacuum to it the idle rpm dropped and it ran rough. With the used replacement if I apply positive pressure the idle rpm drops and runs a bit rough. I think I need to get a NEW sensor which I am not in a hurry to do because of the price. I put the bike back together and rode nearly 400 miles on Saturday with no issues but I didn't get stuck in much slow traffic or short stoplight-to-stoplight situations. The bike still starts to run a bit rough when hot idling but did not sputter and act like it wanted to stall out when taking off from a stop which was my biggest concern before. I am considering buying another motorcycle to keep on the road and maybe tearing the motor down on my wee this winter to do a valve and ring job (i have a lower compression than i should despite correct valve clearances). I'll have to make up my mind as to keeping it or selling.
 

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Low compression can cause your problems.

A leak down test will tell you a lot more than just a compression test, testers are not expensive but you do need a compressor.
 

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Discussion Starter #9
after replacing the IAP sensor and riding about 800 miles over the last 2 Saturdays (while running some Seafoam in my fuel, which was also switched from 93 to 87 octane) It definitely appears that my rough idle and sputtering issue was taken care of.
 

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Discussion Starter #11
Did you find a decent deal on the sensor?
I found a used airbox with sensor on ebay for$30. since the new sensor is $265 i took a chance that this one was ok. Unfortunately the problem came back on a short ride yesterday. I am about to go buy another bike (going back to Honda) and then I'll decide what I'm going to do with my wee.
 

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Discussion Starter #13
as expensive as some of the sensors are and the fact that some parts are no longer available from Suzuki (ECM in particular) i doubt very seriously that I will ever buy another Suzuki. I bought a Ford car once and had nothing but problems with it. Now, it might have just been a lemon but I'm not ever going to buy another Ford either. Just left a bad taste in my mouth. I've owned 2 Honda motorcycles, put 50k miles on them and spent a total of $135 on parts for repairs between the 2 of them. I'm just going to stick to what I know is good.
 
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