will not fast idle when cold

My 8gen with untouched SV's and untouched Wax Unit. Stable idle speed of 1200rpm happens at approximately 50degC or 122degF.

 

Thank you, Grum. That last data point helped me get as close as I'm able to get to all systems go. My fast idle now hits 122F at 1200 rpm. The continuing puzzler is that only sometimes does it idle on its own right from when i hit the starter button when it's stone cold. Often it still does not, and i have to hold open the throttle, sometimes up to a minute, before it idles by itself. It's just not consistent. What does seem to be a trend is that the warmer it is in my garage (it is much more likely to run on its own immediately when the temp is above 46F, but far more unlikely when below, around 39-41). Honestly, it seems like it's getting enough airflow, but not enough fuel at cold idle. I'm guessing that's a function of the ECM. Eeks.

Yes, Terry, I could crank down on the Wax Unit nut, but that will have the same effect as opening the SVs a little more, and been there done that, and it just doesn't give consistent positive results. So, i might be at the place where i'll live with it, since i don't often ride at those low temps anyway.

I feel a little defeated at this stage of the game, but then i remind myself that i am MUCH farther along -- and with a MUCH greater understanding of the idle induction system -- than when i started, thanks to you all. I really appreciate your input. Each post filled in some blank in my knowledge. So thank you all.

 

Have you tried removing the airfilter housing and closely monitored the action of the wax unit acting on the syncronisation plate and linkages starting from a cold engine? Have you tried lubricating the Wax Unit linkages, rods, link plate, shafts etc, and checked for smooth non binding operation? Does the syncronisation plate always return to the warm Idle Stop position set by the warm Idle Adjuster. Can you see that before even starting a Cold Engine that the syncronisation plate is away from and not touching the warm Idle Stop position?

If you are still concerned about cold idle enrichment, then you may need to do some checks on the ECT sensor. This is a two part device with an independent signal to the Instrument Panel and another to the ECM. I know you haven't reported any ECT sensor Fault Code detected by the ECM, but the ECT signal to the ECM might still be drifting within allowable ECM tolerances. So some good continuity checking from the ECT connector up to the ECM should be done along with some good electrical contact and anti oxidant compound like OxGard applied to all connections. Refer to the voltage and ECT resistance checks in section 5 of the Service Manual, Note Reference to a Fault Code of 7 and its corrective action.

Just thinkin out loud!!
Best Of Luck!

 

Yes, that whole airbox is off nearly all the time i'm testing, and i've come to closely monitoring the warm idle plate position in relation to the tip of the idle speed screw. When i started this process, i realized after Terry's input, that i'd run the SVs so far closed that the SV plate was resting on the idle screw even when cold. So that was a helpful data point -- open SVs enough to get that plate away from that idle screw! And yes, i lubed the SV points and the Wax Unit points, and it always seems like it's moving freely and through a reasonable range, so it doesn't seem like the cause is a mechanical binding. And yes, at about 122F, when the tip of the Wax Unit rod gets loose, the plate is resting on the idle screw, and the warm idle speed can be adjusted slower or faster, so i am now comfortably in the range of that component.

See if i have this right from your ECT comments: First, are you saying that the ECT is THE determinant to tell the ECM how much fuel to supply at a given temp? Second, with the ECT sending signals to both instrument panel AND ECM, your suggestion is that what's going to the ECM is either at least slightly incorrect, or that the ECM is doing a poor job of responding to the correct data that it's receiving? I can vouch at least for what's displaying on the instrument panel, since its performance has not changed since i first got the bike. And its behavior during all of this testing and fiddling has not changed. That is one place where i've seen consistency.

If i'm correctly understanding you, my response is that even getting at the ECT sensor seems enough of a pain that, after all my t-shooting, i don't have the drive in me at this point to chase those measurements. It is a reasonable next step, though, and i might do it at some point when this gets to bugging me enough. Btw, a new ECU (that's what i see the ECM getting called here and there) is $2100 on PartZilla!

 

For a cold start Yes.

As mentioned and if you look at the wiring diagram the ECT has two independent sensors within the one unit. It's quite possible the signal to the Panel could be fine while the ECM signal may not, eg and poor connection, intermittent faulty sensor for ECM, could possibly create a value still acceptable by the ECM yet not correct to true engine temp, thus screwing with cold enrichment. The ECT, TPS, IAT and MAP sensors all rely on the 5v VCC Supply (a stable reference voltage supplied from the ECM) as well as the Signal Ground, more stuff that might need checking Refer Service Manual. Sorry if things are getting technical here!

The ECM (As is always referred to in Honda Service Manuals) as complex as it is, is incredibly reliable. It is generally the connections, sensors, voltage supplies and grounds that are the problem cause. High overvoltage from a failure within the R/R is a killer for the ECM.

A few things to check and try!........

I recall having poor idle problems years ago with my 6gen, the cause was water condensation in the tank. Have you got fresh fuel in the tank, this is especially important if you are using Ethanol blended fuel?

Another issue could be old, faulty or fouled spark plugs, these can cause many strange effects, from poor idling to rough running, poor fuel economy etc. Strange, intermittent, unexplainable running problems can be caused by the battery and or connections, so check for clean tight battery connections and a healthy battery.

And something worth trying and not too difficult, is to remove the two large ECM plugs and give the pins and sockets a good spray of something like CRC 2-26.

And also check all the vaccumm hoses for cracks/splits or damage especially the ones going to the MAP sensor and its 5 way junction.

And just to confirm - With Ignition to ON and Sidestand down, your Fi Light is NOT flashing any error code? When doing the SV synch you may have seen an active error code for the IAT Code 9 and MAP sensor 2 these should disappear once vac hoses and connectors are reinstalled after completing the SV synch. (However these codes will now be located in stored memory as historical codes which can be later viewed or erased if need be).

Does the intake flapper on top of the airbox have its vacuum hose connected? If not, refit it, OR if the flapper system has been disabled, confirm the hose is block off and not damaged.

Once again - good luck and hope this helps! Don't have anything else to suggest.

 

Finally bought an ECT sensor, installed it, put it all together and fired it up -- and the coolant temp immediately read about 232F, quickly climbing until it peaked at 270. Let it cool, same thing happened again. Got a refund, bought another one, only this time i did a little measuring first. Both the original sensor and both new ones all test the same, showing about 2.5 ohms between the two leads, and open between all other options, including ground. Also, when i plug each one in, they show " - - " on the gauge, indicating something below 95F. However, with the two new ones, as soon as i touch the brass part of the sensor to ground, they display around 232F, but the original one continues to display " - - ".

Have you heard of this? Did i get 2 bad new ones? They were each about $9, compared to $80-something for a genuine Honda part.

 

Oh dear, I feel your frustration! To be honest I've never had to replace an ECT on my VFR's But $9 for a dual element ECT sounds awfully cheap and possibly nasty!

It's interesting to note when checking the Partzilla web site that the ECT sensor is the same item from 1998 up to the 2014 8gen P/No. 37870-MBG-003.

If you look at the drawing attached you can see the two ECT elements are completely independent (drawing is from a 5gen, 6gen should be identical) and that the element for the Instrument Panel readout absolutely relying on a good Ground through the ECT body and frame grounding. Not so the ECM element, from memory you should measure 5v reference voltage on the Yellow/Blue wire of the ECT plug, vitally important for the ECM element. The Green/Orange being Signal Ground.

Sorry I can't offer much more, but I think that given the importance of the sensor I would definitely hang the expense and go with a genuine OEM unit. That $9 unit sounds Very cheap and suspicious to me, not something I'd rely on long term, even if it did initially work.

Good Luck and sincerely hope for a positive outcome, you've gone through a lot.

 

That attachment of the ECT closeup was very helpful; thank you so much. (Curiously, instead of G/Bu i have G, and instead of G/O i have G/Y. I even pulled back the plastic wire covering to make sure the colors were not faded at the ends.) Nevertheless, all the manual specs, both voltage and ohms, are correct. Still, i ordered a genuine Honda ECT, but until i install that (as soon as this week, because the most accurate test is when the ambient temp is below 44 F, and that is quickly getting away from us here in Colorado), I have a benchmark question for you: What is your highest fast idle speed? I'm already using 122F as a benchmark for when fast idle should subside, but your top fast idle speed will be another good benchmark, to help me make sure that my #4 SV is truly back at its original factory setting.

 

Hi innokente.
Your question kind of relates to how long is a piece of string?
With my 8gen. the cold idle starting rpm varies greatly on ambient temperature the wax unit is effected by both ambient and coolant temps.
So on a hot summers day first cold engine start, cold idle might be bearly above hot idle (1200rpm). And on a very cold winters day I might see anywhere between 2500 to 3000rpm.

Just reading this again. An important statement you've made has come to mind. The Instrument Panel sensor and ECM Coolant sensors within the ECT Are very different elements and completly Independent. For the Instrument Panel Sensor to work the body of the ECT MUST be GROUNDED.
Without the Ground reference the Instrument Panel is seeing an Open Circuit Sensor.
Temp Specs for the ECT to Instrument Panel sensor are 2.3 to 2.6 Ohms @20deg C
Temp Specs for the ECT to ECM Coolant sensor are 2.1 to 2.6k Ohms. (2100 to 2600 ohms) @80degC and 650 to 730 Ohms @120degC.
NOTE - The Instrument Panel sensor has a connection through the element to Ground via the ECT body. The ECM coolant sensor has NO connection to the ECT body.

Info - The ECT Fi DTC Code of 7, is Only for the ECM sensor, Not the Instrument Panel sensor.

Again - Good Luck with everything.

 

Thank you so much, Grum, for hangin' in there with me. The string example -- that didn't seem 100% legit until you said that the wax unit is affected by both ambient and coolant temp. And i've been watching the behavior of my bike over the last week, with temps varying by 40F and, yes, the top fast idle speed does vary acc'gly. On to all your specs -- yes, i'm tracking all of that and have watched for those requirements, so we are on the same page (now) with that.

BUT, the fast idle seems now to be consistently working! With the original sensor. It has worked at 53F, and also 41, 34 and 32, where it wouldn't before. What is different? After those two cheapies didn't work, i ordered a genuine Honda item, but because awesome weather was coming, i reassembled the bike with the original sensor and have been riding it. The genuine Honda new sensor came today -- but why change it if it's working? So, the ONE thing i changed was this -- I polished the old sensor with steel wool. It was pretty dark, with what i take to be natural residue from 17 years of coolant immersion. In your experience (i personally have never heard talk of this), is it possible or at all likely that that was creating enough effect on the sensor's behavior that it is now working but wasn't before the polishing?

 

Good news to hear your fast idle seens to be sorted. It appears the most common cold fast idle issues seem to be the Wax Unit or its plates and linkages causing stiction due to gunk or corrosion.
ECT requires good ground bonding of the body of the unit ONLY for the Instrument Panel readout. The ECM sensor within the ECT doesn't need this ground.
Good luck hope the bike continues to run well.

 

Maybe the action of unplugging and re-plugging the original ECT was enough to clear a bit of corrosion on a terminal somewhere. Stranger things have happened. Regarding tarnishing of the sensor unless a thick coating had built up that was causing an insulation/delay then I doubt that would be a factor.