M8 , idle speed
Advanced
Joined: Sep 2020
Posts: 79
Likes: 28
From: Navarra
You must be an H-D service tech. No, they all don't do it. Fortunately, found another post with identical problem. Found a hairline crack in the cheap plastic intake manifold. Shame on you H-D. $20K bike and plastic manifold. Replaced it with an S&S aluminum one. Good coasting idle, just like my 2 previous M8s.
I'm taking it to the dealer today for the 10k miles inspection and will certainly ask them about this.
Thanks for the heads up!
Stellar HDF Member
Joined: May 2006
Posts: 2,809
Likes: 4,207
From: NC
Well, mine certainly does it and I honestly thought that all of them did it because the MoCo wanted them to do it. I don't pay much attention to it, anyway...
I'm taking it to the dealer today for the 10k miles inspection and will certainly ask them about this.
Thanks for the heads up!
I'm taking it to the dealer today for the 10k miles inspection and will certainly ask them about this.
Thanks for the heads up!
M8 Idle Issue Solved - Harley Davidson Forums (hdforums.com)
Stellar HDF Member
Joined: May 2006
Posts: 2,809
Likes: 4,207
From: NC
The job is not technically difficult, but it is annoying getting to the hex bolts on the two intake ports. I had to remove the coil to access the lower bolts. Good video below. The shop manual is also your friend.
Stellar HDF Member
Joined: May 2006
Posts: 2,809
Likes: 4,207
From: NC
Interesting. I had to call Fuel Moto because a tune wiped out my cruise control, so I asked about the coasting high idle. Lucas said some bikes do it by ECM design. I'm glad mine was a cracked intake manifold that was fixable. I hated coasting to a stop with an idle at 1.5 - 2K. Sounded downright silly.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Tourer
Joined: Mar 2016
Posts: 275
Likes: 65
From: So Cal
Interesting. I had to call Fuel Moto because a tune wiped out my cruise control, so I asked about the coasting high idle. Lucas said some bikes do it by ECM design. I'm glad mine was a cracked intake manifold that was fixable. I hated coasting to a stop with an idle at 1.5 - 2K. Sounded downright silly.
Road Master
Joined: Feb 2018
Posts: 1,197
Likes: 1,852
From: England
This was a subject bought up by more than a few new car owners in the UK, why the revs seem to "hang" when you're slowing down by changing to a lower gear or coming to a halt. The explanation given was this is to enable the motor to burn any excess fuel in the inlet manifold as the car slows so as to keep the emissions lower than they would otherwise be.
