Surging idle on cold start up

hossman

.040 Over
Joined
Oct 20, 2013
Messages
90
Location
New Jersey
Ride
2025 Rocket 3 GT Storm
Soon as I start my 16 Roadster after it's been sitting awhile, the bikes rpm's surge up and down almost stalling and does that until it warms up. Any idea what this could be? Throttle bodies out of balance? Bad throttle position sensor?
 
Mileage on the bike? Has it had its first service?

Some degree of what you describe I've heard every single rocket started near me do.

But it generally should fire, kick to 1200ish on a cold start and slowly fall to normal with a few up/down hiccups when doing the idle speed adjustment as it crosses the 950-1000 rpm mark.
 
Mine (a 2013)will initially fire up and rev high, but I am pretty sure this will diminish as the weather warms. The ECU see the engine is cold and senses the air is cool, so it prepares a high idle on start, but realizes the engine will run fine at normal idle so kicks it down after a few seconds. Like pulling the choke out on that old bike you used to have. But now the ECU does it for you.
 
2,100 miles and the bike had it's 500 mile service. The bike normally would stay around 1100 rpms when cold and gradually drop as it warmed up. Now it's dropping to the point of stalling and I guess it tries to raise the rpm up and back to dropping to the point of stalling.
 

I think as others that an ISCV reset is in order. If only to eliminate a suspicion. It's possible during the service something was disturbed.
 

I had similar at one point. If I remember right it's about the time I adjusted my TPS, but I can't say for certain that was the cause I did a few other things at the same time.
 
Mine did the same. Only if I took off hard and came up to a hard stop and pulled the clutch, it would stall. TPS adjustment fixed it.
 
warp9.9 said:
Proably just needs a throttle body balance/check and a full ISCV Reset she pretty new things are settling in.
Click to expand...
I did that to the Rocket X at the 500 mile check and it fixed it. Throttle body balance was off by a lot. Was a little surprize to find the balance that far off on a new bike. surging idle disappeared and overall performance greatly improved.
 
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