Occasional Fast Idle

[Thrud]

Occasionally, when I pull up to a stop and sit idle the engine speed will creep up to about 2,000 RPM.  This occurs after the engine has reached operating temperature.  I do not have vacuum leaks because I recently replaced all vacuum hoses, carb vacuum plugs, fuel and air rail O-rings and intake O-rings.  Carb sync is not an issue.

I recently replaced the coolant temperature sensor behind the radiator because I heard that a faulty sensor could cause the ICM module to think the engine is overheating and increase the engine speed at idle.  The problem appeared to disappear for awhile but has since reappeared.

Engine idle speed is correctly set at 900-1,000 RPM at operating temperature.  There is no binding in the throttle cables and the throttle grip is adjusted for the proper amount of play.

This problem has me perplexed since it happens only occasionally.  Should I look into the ICM module?  I searched the forum, and I can't seem to find anyone reporting other problems that may cause this situation.

Steve

[gordonv]

I had this same thing happen on my GL1100. Come off the hwy to a stop light, idle, and it doesn't come all the way down.

I did/do 2 things.

Carb cleaner.

With the bike stopped, foot on brake, I have it in gear and slowly release the clutch lever so the engine starts to bog down, and then the clutch back on before it stops. Usually this will pull the rpm back down to something more reasonable, like 1K.

Never tried to look for vacum leaks, which was most likely what the problem was, since in a few more seconds I'm off ridding again, so who cares (yet)?

[Thrud]

Unfortunately, blipping the throttle doesn't help.  The bike lurches when putting it into gear at 2K RPM.

Steve

[Denny47]

There are two throttle cables to your grip. One is for acceleration, the other is for return. If the return cable was out of adjustment or broken, would this not be a possible cause for the excessive engine speed? I'm not sure myself, just bringing it up.

[vic]

I had this problem and decided to deal with it last Fall.  I changed every vacuum hose I could find to rule out any leaks and then changed the engine coolant temp sensor like you did because it can be one cause of the fast idle.   At the time, I also thought my idle knob on the right side couldn't be turned out anymore to lower the idle until I reached in with some needle nose pliers while syncing the carbs and found I could turn the idle lower.

So now, the idle is holding at a hair under 1,000 RPM (where I set it) but I won't be able to tell if I really fixed this problem until the ambient temps go up and the bike gets really "heat-soaked".  It was when the bike was "heat soaked" that my idle would shoot up like you are experiencing.

Do you have anymore "play" in your idle knob to turn it down when you experience the fast idle?  If you do have "play", turn it down when the engine is good and hot and see if the idle holds.  If you think you can't turn the idle knob anymore (like I did), reach in with some needle nose pliers and see if you can't get it turned down with the pliers. 

After saying all this, I will have to wait for a few long runs before I can determine whether my fast idle problem is fixed or not.

[Ricky-D]

I don't understand the remark that carburetor synchronization is not the issue, but regardless,

Carburetors are your problem.

Whether it's vacuum leak, sticky parts, loose system parts, improperly attached parts, the problem lies with the carburetors.

You should redouble your efforts to find the solution.

Thinking that this (or that) specific item is not a problem will tend to point you in a direction that may not lead to a correction of the problem, but simply start you on a path of replacing parts that are not necessarily needed.

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