Bike with problem is the one in my sig.

A few weeks back I did a few hour ride ( one way ) in 85 degree temps and had trouble keeping the bike running even at speed when I let off the throttle. ( Posted a thread on it ) Tried the carb cleaner up into the IAC port while cycling the ignition. A little crap came out but not too bad. Bike seemed to run fine after that but it was pretty much short rides like an hour or so one way. Yesterday I went on a longer ride ( 88 degees about 2.5 hrs one way ) and the trouble started again. Not only will it not idle when I come to a stop but it will die while at speed in any gear when I let off the throttle. Roll on the throttle just a little bit and she's running ( at speed ). Got home and took the air cleaner off and cleaned the IAC port again. It seemed to be pretty clean. Started the bike and it still wouldn't idle. Needed to use the throttle to get it started.

This morning I tried it again ( after it sat all night ) and it started and idled normally. Anybody have an idea where I should start to solve this issue? Temp sensor? TPS? Crank position sensor? Something else? Where should I start first?

Note: Oil temp was around 225 - 245 when I had the trouble.

Thanks for your valued input..... Mike

 

You can upbolt the IAC and clean that area up completely.
Two bolts and the thing comes off. You can verify clean thend.

 

Do IAC problems only happen when the engine is hot or is it more of a consistent issue once they get gummed up? Bike seems to run fine when cool


Gunny can you give more detail on how to remove IAC or where I can get info? I don't have a service manual. Thanks......Mike

 

Kind of a long read, but jump to the last paragraph to see the solution I found for similar problem on the wife's 2006 Sportster. Three years now and it has been fine after replacing the crank position sensor.


2006 Sportster 883L (carb)

The bike was purchased new in June 2006. From day 1, it had an intermittent problem. Occasionally, when it was ridden in warm weather and motor was warmed up, it would cough/fart thru the carb when trying to start up from a stop light. To keep the bike from dieing at lights, you had to keep twisting the throttle. Accelerating hard, there was a flat-spot where the bike would just limp along for quite a while before taking off.

We took the bike back to the dealer and he explained that HD sets these bikes far too lean in order to meet EPA standards. He rejetted the carb – replacing the low speed jet with a #48 jet. (Stock is a #42.) He did not drill out the plug for the mixture screw, so I know he did not adjust that.

The bike ran okay for a short time, but then the same intermittent issues started again. I installed the SE intake/breather in the spring of 2007. The bike ran fine all 2007, so I assumed installing the SE intake had solved the problem.

Fast forward to 2008, and the same intermittent cough/fart thru the carb starts again, and all the other symptoms. I took the carb apart and found no crud and no obvious problems. I put in a #45 low speed jet, drilled out the mixture plug, and set the mixture screw 2 ¾ turns out. This made no improvement and all the issues were still there.

I tore carb apart again. Replaced the needle and spring with the needle and spring from a Dynojet kit. (I did not drill out the hole in the slide.) I put the needle c-clip in the 4th slot from the top and put in 3 washers. I also replaced the breather washer that had come with the SE intake kit with a couple washers that were a little thinner. (The washers in the SE intake kit were slightly thicker than 1/8” - .137”. I replaced them with washer that were slightly thinner than 1/8”) I thought this would allow the carb to fit a little tighter in the gasket between carb and manifold, perhaps giving a better seal.

At the same time, I replaced the crank position sensor because I had heard of similar issues to mine being caused by a bad crank position sensor.

After all these changes, the bike appeared to be running absolutely flawlessly. Now the question was, did the mods to the carb solve the problem or was it a bad crank position sensor??? I ran the bike a few more days to make sure the intermittent problem is really gone. Then I put the original crank position sensor back in and ran it for a while. Sure enough, the intermittent problems returned when the bike was hot. I put the new sensor back in and it has run flawlessly all season. Conclusion – Crank Position Sensor was the culprit!

 

It could also just be a bad IAC motor. They are well known to fail, and more so with more miles! As the bike runs fine after a key cycle, it seems most likely it is a faulty IAC.

The threads in the IAC motor are suseptable to wear. The ECM uses a "counts" method to determine IAC position. ( there is no feedback on an IAC motor, only a "running counts" for each key cycle.) When an IAC "looses" counts, the ECM attempts to return to a known position, but if through wear, the motor has lost counts, the ECM can actually drive the pintle ( IAC air control) into the seat and the engine doesn't have enough air to run.

A quick summary of IAC motor movement! The IAC system is used for modes other than jsut IDLE. Every throttle input, also moves the motor position. This is done to control DECEL air rate and also to act as a throttle follower ( slight increase in airflow) for every throttle opening from closed. Throttle follower is also active for ALL throttle positions. The bottom line to all that, is the motor is continually moving while running. The longer you run the engine the more chance to "lose counts."

When you turn off the key and turn it on again, the IAC motor has reset!
The ECM knows the position after a key cycle.

I have also had IAC motors that lost counts, after even a short run!

Also as you can "push" or move an IAC pintle when they are removed from the housing, you can damage the threads just by forcing them back in!

I am a retire calibration engineer, and have lots of "experience" with IAC motor issues!!

One of the major advantages of Drive-by Wire, is you don't have an IAC motor, with drive by wire!( Of course DBW is not without issues too!)

 

FBRR thanks for an informative post. Do you mean by shutting down the bike by turning the key off and reset the IAC motor then it would start and run fine 'til it runs long enough to lose count again? When I'm having trouble it will not restart or run normally until the motor sets and cools for a period of time meaning I have to keep the throttle slightly open to keep it running. Does heat have anything to do with my problem? This problem is somewhat intermittent but there seems to be one consistent thing when it acts up and that is running it for a couple hours or so and engine oil temps at least 225 degrees. Have not had any problems yet on short rides.

 

If you cycle the bike on and off without starting it you can hear the IAC run after you turn the power off. Once that completes the bike should start if it's the IAC losing counts. There's the issue of why it's losing counts though. If the IAC is failing to step then it may well fail to do so more often when hot. IAC's aren't terribly expensive, but they aren't exactly cheap either. Heat I would expect to have more to do with a clogged IAC passage so I would want to make absolutely certain that's not the problem before replacing the IAC. I would also want to make sure it isn't a problem with the connectors to the IAC.

 

So I guess the best way to go for now may be to try removing and thoroughly cleaning the IAC and to make sure connections are good then go from there. I hope this doesn't turn into chasing a ghost. I was hoping that someone out there had the same exact symptoms as what I'm having and could save me some time on troubleshooting. That would be too easy though. Thanks again for the input guys....Mike

 

Unless the IAC motor is completely shot, it should reset with a key cycle ( on-off 15 sec or so-on). If it doesn't start hot, it sounds like something other than an IAC motor! As someone suggested, maybe the crank sesnor. Heat will affect the crank sensor!

 

2007 models had a bulletin released about the wrong loctite being used on the throttle stop screw making the idle erratic low/high depending on which way the screw decided to turn. Throws the whole system out of wack.
Also replace the TPS and it is easy and cheap to do and they do go faulty.