Started up my '98 FLHTCI this morning and everything was good. Half a mile down the road it started revving real high and wouldn't slow down. Turned around and took it home, still revving high the whole way. Any idea's of what could be going on? It was a little above freezing this morning if that makes any difference.
Thanks, Rob

 

I would look for a tear in the intake boots

 

Check to make sure the throttle body isn't sticking open. Might be gummed up.

 

First check your throttle cables...Intake leak is also possible Also I have seen some worn out throttle plate shafts...If that is the case you will have to replace the throttle body.

 

You may want to have this moved to the EVO section.

1998 is M&M EFI. There are a few reasons to get a high rev. First thing is to pull any codes that are stored. The service manual will tell you how to do that. After that list them here. You can also reset the ECM by pulling the fuses, or diconnect the battery for 30 min to 1 hr. then resynch the Idle Air Controller to the ECM. But pull the codes first otherwise if you have a more serious issue it will only happen again.

You also clean out the Throttle Body intake and pay special attention to the two small holes on the inside, top of the intake. Spray them out with throttle body cleaner well until they run clear.

Other reasons for high idle are failing Engine Temp Sensor, IAC, TPS, or intake leak. You have to chase them down one at a time.

 

Having the same issue with my 97 Ultra. I too need to do my homework, but I believe it might be related to the temperature sensor. Dealer reset idle settings and that didn't cure it. Runs great in warm weather, but in cold.... well, high idle is a kind description.

 

I went through 3 temp sensors on my '97 RK. There have been several up grades to the sensor. Make sure you have the latest one.

 

On an EVO of that age I'd definitely recommend new intake "O" ring seals.

You could have throttle cables issued and they should replaced also.
(I had mine replaced just as PM).

Hopefully you'll find simple problem such as a ETS or a TPS and not a serious issue with the MM EFI.

Good luck.

 

Check the throttle body seals.
You have a vacuum leak. You could spray water to check for idle interruption to determine the leak area

 

Have you tried pulling any trouble codes? ETS, and IAC often will not show up as a code. You can test the ETS by checking the volts and ohms across it based on ambient temp.

The test for the IAC is a simple Go/NoGo test. With a cold bike tun the key switch on while observing the IAC. Does it move? Then start the bike while watching the IAC. Shortly after starting the bike the IAC should move in (toward the TB) and the idle should drop down. If the IAC does not step then it needs to be replaced.

If neither of these tests show a faulty sensor then you check you leaks.