98 ULtra FLHTCUI High/Erratic Hot Idle : V-Twin Forum: Harley Davidson Forums

Ted Zackro · 07-03-2009, 09:01 PM

I have a 1998 Ultra FLHTCUI with SE A/C and Slip-ons.
The bike starts up from cold and idles ~1900-2000 RPM and then drops down to ~ 1000 RPM...Revs back up,
drops down to ~ 1000 RPM...Revs back up,
drops down to ~ 1000 RPM...Revs back up...
What could be causing this?

I was able to ride the bike to have the indie look/listen to it and it didn't have any fuel starvation problems accept the annoyance of the high/erratic idle.
He thought it was a fuel pressure problem...also never saw this problem before. Indie was a technician at a Harley dealership.
Any ideas out there on what is causing this?
Thanks,
Zman

Dr.Hess · 07-04-2009, 10:39 AM

Can you pull a code from the computer?

In general, things like this happen with EFI systems when a sensor or the wire to the sensor goes out on you or has an intermittant issue. Could be a throttle position sensor, intake air temp sensor, cylinder head temp sensor, oxygen sensor it your bike has one, vacuum sensor if it has one, etc. Of course, check for intake leaks. I dunno about fuel pressure. In my experience, you either have it or you don't, not a changing one.

I seem to recall reading other people with one of the temp sensors going out giving similar issues.

Ted Zackro · 07-04-2009, 03:54 PM

Hi Doc,
When I try to pull the codes from the computer all i get is fast blinking...,
followed by a pause...fast blinking,
followed by a pause...fast blinking,
followed by a pause...fast blinking...
I assume this means that no trouble codes are displaying?
Zman

Dr.Hess · 07-04-2009, 04:03 PM

Zman, I dunno about your codes, but that sounds like "no codes" for most early EFI systems. I'm not a HD EFI guy. I built my own. I do seem to recall that a temp sensor may or may not throw a code when it's bad with some of these OEM HD EFI's. See, if the computer sees the thermistor (temp sensor) as high or low, it might think that's just what the current conditions are and change the maps or whatever accordingly.

Ted Zackro · 07-04-2009, 05:21 PM

Yeah, Doc,
That's what my local indie also tells me. I can start changing out sensors but that can get real expensive fast!
He also said this is what a HD Dealership Service department would do until the problem is fixed and charge for all replaced parts plus labor...ouch.
Happy 4th,
I appreciate you responding today!!!
Zman

tombardier · 07-16-2009, 01:09 PM

Hi Zman. I have a '98 Road King Classic with the exact same problem you are having. When engine reaches operating temp idle goes up and down, up and down, ect. I read your comments back and forth with Dr.Hess. I just installed a new cylinder temp sensor. When I first rode off it seemed like the idle was slower and steady but after reaching operating temp it was back to the old up and down, up and down. I don't know what to try next. If you come up with something please let me know and I will do the same.
Tom