I have an 03 Fatboy with fuel injection that I recently picked up. It has 28,000 miles on it and appears to be well taken care of, it looks brand new.


It starts right up and idles fine. It runs down the road perfect and feels strong. But after it warms up, it starts to idle rough when I slow down and come to a stop. When I take off it picks back up and runs great. It only sounds rough when it's idling after it warms up. After it cools down and I start it up again, it fires right up and idles fine until it warms up going down the road and then it idles rough again when I come to a stop.


It has a Screamin Eagle stage 1 air cleaner and Rinehart racing exhaust. It doesn't have a fuelpak or tuner that I can tell. (I'm a first time Harley owner so this is all new to me) I'm the 3rd owner. The first owner had everything installed on it and the second owner bought it in 2007 and he told me the original owner said he had everything installed at the Harley dealership and they set the tune.


I took it to a local indy shop down the street and he checked the plugs and said they were fine but said since there was no warning light that he couldn't read a code off of it and he doesn't have the equipment to work on fuel injection models and I would have to take it to a Harley dealership.


Does anyone have any ideas of what might be causing it or what I should look for? I'm no mechanic so I'll end up having to take it to the dealership but I'd like to get an idea of what it might be so I'll know a little of what I'm talking about to make sure I don't get taken to the cleaners.


Here she is.

 

I had the same problem earlier this year. Replaced the Crank Position sensor and Vehicle Speed sensor but the problem remained. Finally identified the cause. Faulty Idle Air Control valve (IAC). If I remember correctly the IAC valve is roughly $50.00 bucks. This is an easy DYI project. No need to add labor cost.

My next piece of advice is to buy a Harley Service Manual. It will be the best money you'll spend on the bike.

 

I would also look at the IAC or possibly a vacuum leak in the intakes.

 

Thanks guys, I'll look into the IAC and check it out.


Today I removed the screamin eagle intake and noticed the two rubber breather lines that run back into the filter were cracked and split. I'm no mechanic but could this cause a vacuum leak and make it idle rough?


I ordered an Arlen Ness big sucker kit to replace it since it doesn't use external breather hoses and I can still use my stock filter cover.

 

The breather tubes from the rocker covers go to the area upstream of the throttle body, so they have no impact on the intake manifold vacuum.
You need search for leaks downstream of the throttle butterfly.

 

Thanks for the info, I wasn't for sure. Once my new air intake kit comes in Tuesday I'll get it installed and I'll fire it up and use a propane torch to spray around and see if there are any vacuum leaks. I went ahead and ordered a new IAC valve a few minutes ago and I'll get it installed to see if that was the problem. Hopefully that's it and it'll be a fairly cheap and easy fix. Much better than having to take it to the Harley dealer 40 mins away.

 

The Harley Electronic Diagnostic Manual states that the IAC valve resets itself each time the ignition is switched off then back on. This was key information which allowed me to isolate my idling problem.

When replacing the IAC valve, clean the cavity that the valve plunger inserts into. I use a Q-Tip with brake cleaner sprayed onto it. Carb cleaner is not recommended as it can cause damage to the MAP sensor.

 

I don't understand. How did the IAC valve resetting itself help you to isolate the problem? Is there some way you can check it and the other sensors to tell what the problem was?


Thanks for the heads up on cleaning the cavity with brake cleaner, I'll be sure to do that.

 

After a lengthy highway run, my engine would idle erratically when coming to a stop however, if I switched the ignition off, then restarted the bike, it would idle correctly. Reading that the IAC resets itself each time the ignition is cycled fit my symptoms and narrowed the diagnostic parameters.

Your symptoms may differ slightly but I still suspect that your problem is with the IAC valve. Sometimes removing, cleaning and re-installing the valve can cure the problem.

 

Try cleaning the existing IAC sensor needle with brake cleans and q-tip before you replace it. They are known to have build up and stick. I would still replace it, because cleaning it is only a temporary fix. At least you will know before you replace it..