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Fast idle

Started by northern, Friday, 21 July 2017, 04:56 AM

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Mates, need advice of those who know.

I have a problem with fast idle, when engine is cold:
When I start my bike, it starts with higher revs, but instead on 30 sec at 20C°, revs are higher only for 3secs, and then drop to normal, which on a cold engine are less then 1000rmp. At this moment, I manually add revs (by idle revs knob) to ~1200 and as far engine gets hotter and hotter (during riding), revs are going up and up. Up to 1500. At some moment, on a traffic light, I have to lower idle to 1100-1200.

How I understand this situation: there is a problem in my fast idle system.
Do not remember exactly when it happened (long time ago, I just was lazy to deal with it), but probably after I was synchronization throttle valves.

Yesterday I check TP and STP sensors settings (according to service manual 4-35 and 4-43). Voltage on open-close positions of both sensors, was quite perfect. Also STV actuator seems to work, because STV was moving during self test, after ignition was switched on...

Tomorrow, I want perform a FAST IDLE INSPECTION (service manual 4-65)... Does anyone have done this, or have similar experience and can give me some advice what to be prepare with?  :confused1:
Any information is apraitited.


The timing of your post is perfect for me. My problem is similar to yours. When starting the idle drops to just below 1000 rpm and slowly (after a minute or a little more) rises to 1100. Ambient temperatures are above 20 degree celsius. Here comes a possible clou. By accident I hit the kill switch just after starting (less than 1000 rpm). When I restarted, the fast idle behaved perfect. RPM goes to 1400 plus and after 30 seconds down to 1100. Since then I have repeated this several times. Always behaves perfect after hitting the kill switch and restarting again.

My TP, STP, and STVA are also working/set up near to perfect. Tomorrow I will do an electronic reset (as I described here in another post). If that doesn't help, I'll inspect the ECU (ECM) contacts. Would be great if someone here has any ideas, experiences, and hopefully a solution (before the cold season kicks in at last)

Would be cool if you try the kill switch thing too. Please report.


I'm skeptical, but I will try kill switch tomorrow. Will let you know.

What is "electronic reset" in case of 14?  :confused1:


skeptical is always good!

I'll tell you about about the reset tomorrow (today). Need to get to bed urgently :)

T 24

I have my version of the same issue. After cold start she runs 2-3 seconds slowly and stops, and after second start she runs nice 1500 rpm. This is not happening in every start and always under + 8 degrees celsius. Like the "cold idle system does not have enough time to activate". if you give her a little bit throttle during that 2-3 seconds slow run, she keeps on running 1500 rpm.


I have the same issue, when ambient temps are under 20C it will stall. I always let it run for 2 minutes after staring before riding, so it doesn't cause me any problems.



I had this years ago & fixed it without changing any parts, trying to remember how.


Quote from: northern on Friday, 21 July  2017, 05:38 AM
I'm skeptical, but I will try kill switch tomorrow. Will let you know.

What is "electronic reset" in case of 14?  :confused1:

The electronic reset did not solve the problem, but here is how you do it anyways:

disconnect the ground cable from the battery
turn on the ignition (don't start engine) so the capacitors in the system discharge fully,  ECU's temporary memory (where it stores adjustments) gets cleared as well. Leave it like that for 5 minutes.
turn ignition off
reconnect ground cable of the battery
turn ignition on
fully open and fully close the throttle, repeat
without touching the throttle, start the engine and let it idle a couple minutes
take a ride


So, seems I solve this issue, but I'm not happy, cause I have new issue... :frustrated:

According to service manual, while ignition is on:
"...Open the secondary throttle valve fully by turning its link with the finger. With the secondary throttle valve held at this position, easure the output voltage of TP sensor...
... TP sensor output voltage: 1.195 V..."

I use pins, to connect circuit tester to TP and STP sensors wiring, and ajast TP sensor voltage by turining bolt marked with red arrow until TP sensor voltage was 1.195v, while I manually, through the air box, completely open Second throttle valve.

When I put all parts together, and finally  manage to start engine, fast idle was much more like it should be.
But, I discover new issue, which kill my day - battery is not charging, and I can't start bike by itself  :thumbs_down:. But this is other topic...

Tony Nitrous

Interestingly on a Gen-1 Hayabusa, a similar size / age / injected / Suzuki, the fast idle is mounted on the bars and looks like an Old Skool choke lever. The little lever controls the revs on a cold motor, looks (and feels a little) just like a choke on some of my past bikes but its just a crude and effective way to raise the revs.  A thing of the past now I guess.


Today I can confirm, what "fast idle" is OK now. After the start, it was ~1700rpm for half a minute, and then start slowly drop revs until normal.
So if you have issues with your's bike fast idle:

  • Check and ajust TP sensor voltage open and close
  • Check and ajust STP sensor voltage open and close
  • Check and ajust TP sensor voltage, while Secondary Throttle valve is fully opened. It should be 1.195V (mine was ~1.12V). If it's not OK, calibrate it using adjusting bolt (my previous post)
Hope it will help someone in future  :hat:


Nice one, took me months to solve mine when it did it. I think I solved by just adjusting both TPS, so the same thing as you really.


I'm also having a fast idle problem . As in it doesn't work at all . Starting from cold can take a few attempts .
I'm not sure exactly how the fast idle works and if in fact it's totally electrical or there is some sort of mechanical part as well . However I've got the tank off at the moment to synch the throttle bodies and found this (see pic). This is in the centre of the injectors and is not controlled by anything . It moves around by touch and the little wheel is not in any sort of track . The L shaped bracket does look a little bent . Any clue please ?
'04 GSX14,'81 Z1000ST,'71 Dodge Charger Superbee


Go to the downloads and get the Manuel and read through before you do work on the bike your not sure about as a first thing.
All info you need on this in section 4-62 onwards of the Manuel.
For balancing the throttle bodies I think 1 (2 or 3)is set(like with carbs)
The outside pair's are adjusted from above but to sync the 2 halves the adjuster is underneath a bit if a pain to get to but that's where they are located.
You should probably check the tos and stps and throttle cable adjustnent before syncing the throttle bodies as all this should help your cold starting .
The warming up higher revs is controlled by the ecu but the things listed above affect the readings used by the ecu.
Hope that helps
only a slightly modified gsx1400
oh and a standard one too

Sethbot Postwhore


Thank You Seth.
I'lll have a read of the ifo in the downloads before i start attacking things with a screwdriver... The bike has been subject to a previous enthusiastic amateur mechanic who's fiddled with pretty much everything.
I had the bike on the dyno at John Warringtons and he confirmed that at idle the lh two throttle bodies were 'doing nothin'.
I've got some vac gauges and although i've used them several times on carbs this will be the first time on injection. I guess the principle is almost the same tho.
'04 GSX14,'81 Z1000ST,'71 Dodge Charger Superbee

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