1998 VFR800 idles around 2.2k RPMS

[Brayden]

Hey it’s been a while since I’ve put a topic in this group but I have been trying to diagnose this problem now for a long time. My bike will start up around 2k rpms and stay there once warm. I have taken the air box off a million times so I don’t want to take it off again. 
Here are things I’ve done or tested:

New  Spark Plugs

New Coils

New Battery

New ECU 

New Stator

New PAIR Solenoid Valve

New Throttle Body Boots

ALL New fuses

New Air Box(with air box boots)

New Air Filter

All relays are functional 

I have tested the one way valve and it’s operational 

I have checked the timing, and that is all good and timed correctly. 
I have checked the TPS and it is very functional

All of the vacuum hoses have been tested for leaks 

Have tested the bypass control solenoid valve and it’s operational 

I have looked at the throttle cables and they are “within spec” by the book. I can’t tighten them up any more without the throttle sticking and not flicking back
 

So here is the story now. I start up the bike let it warm up, drive it around the block a few times. I get back and it’s still idling high. However which is very weird when I roll the throttle back the other way the idle goes down but the idle is still sporadic but not as bad. As soon as I let go of the throttle from that position it goes back to high idle around 2.2k RPMS. 

[Presson]

Turn down the idle? Starter valves?

[Brayden]

2 minutes ago, Presson said:

Turn down the idle? Starter valves?

The idle screw is completely backed off the plate. Also whenever I try to adjust the starter valves with a guage it doesn’t seem to be working when I turn the screw? So would something else prevent this??

[Presson]

The first thing I would check now is throttle free play. Back off the adjustment at the throttle grip

[Brayden]

5 minutes ago, Presson said:

The first thing I would check now is throttle free play. Back off the adjustment at the throttle grip

I have backed off the adjustment. I have it all the way back 

[Presson]

Oh, and check the wax unit fast idle mechanism isn't stuck. Give it a wiggle and some spray lube; sorry that probably means airbox off again . That has been known to give the symptoms you described.

[Brayden]

1 minute ago, Presson said:

Oh, and check the wax unit fast idle mechanism isn't stuck. Give it a wiggle and some spray lube; sorry that probably means airbox off again . That has been known to give the symptoms you described.

My bike doesn’t have the wax unit. It’s a 98. Also no worries the air box has been left off for these reasons lol

[Presson]

You have been incredibly thorough going through everything else. It's going to be something simple and mechanical. I reckon it's highly likely to be the linkages on the wax unit are slightly sticking/ corroded. Normally fixed by a good wiggle and lube. Sometimes just washing with hard water over several years can cause the problem.

[Presson]

Ah, a 98. So now I don't know

[Brayden]

Just now, Presson said:

Ah, a 98. So now I don't know

Alright well I appreciate the help. If you know anyone who might help don’t hesitate to holler please! Thank you

[Presson]

Hey, Captain 80s, Mohawk, Terry or Grum, any ideas on this one?

[Terry]

The idle speed is controlled by airflow into the engine and with the throttle closed, should rely completely on the starter valves. I know on my 6th gen the starter valves have two ports, one is full open and the other has the plunger mechanism that varies the airflow, so you can't completely stop airflow entering the engine. 

 

Given the symptoms described your issue is either a leaky vacuum fitting (which I think you have eliminated) or the throttle itself. I had an issue where I managed to trap a vacuum hose on the throttle mechanism and that stopped the throttle closing fully, and your description of pushing the right grip closed and dropping the idle sounds consistent with that. My suggestion is to take the airbox off (again, we've all been there) and visibly check the butterflies, and look closely at the linkage between the butterflies and at the throttle drums for anything getting trapped. IIRC there is a throttle stop screw (which the manual states must not be adjusted) on the side opposite the cable drum, that is where I pinched a vacuum hose. The butterflies should be sealed up tight and should "snap" shut when you release the throttle. You should not be able to feel any vacuum with your hand sealing the intake port with throttle closed. 

[Brayden]

17 minutes ago, Terry said:

The idle speed is controlled by airflow into the engine and with the throttle closed, should rely completely on the starter valves. I know on my 6th gen the starter valves have two ports, one is full open and the other has the plunger mechanism that varies the airflow, so you can't completely stop airflow entering the engine. 

 

Given the symptoms described your issue is either a leaky vacuum fitting (which I think you have eliminated) or the throttle itself. I had an issue where I managed to trap a vacuum hose on the throttle mechanism and that stopped the throttle closing fully, and your description of pushing the right grip closed and dropping the idle sounds consistent with that. My suggestion is to take the airbox off (again, we've all been there) and visibly check the butterflies, and look closely at the linkage between the butterflies and at the throttle drums for anything getting trapped. IIRC there is a throttle stop screw (which the manual states must not be adjusted) on the side opposite the cable drum, that is where I pinched a vacuum hose. The butterflies should be sealed up tight and should "snap" shut when you release the throttle. You should not be able to feel any vacuum with your hand sealing the intake port with throttle closed. 

So I do have when you mean when the throttle “snaps” shut. I can do that and the TB’s seem to fully close. If you can see in this picture at the screw I circled when I “snap” the throttle some linkage hits this screw. Is this the screw you’re talking about that’s non adjustable?

[Terry]

That is the non-adjustable throttle stop. If the throttle drum is hitting that screw firmly with a click then it seems you don't have anything caught up. I was wondering if during the process of checking the vacuum hoses for leaks, one had been mis-routed and was fouling a linkage. That would explain "when I roll the throttle back the other way the idle goes down but the idle is still sporadic but not as bad". Unless the throttle was being hung-up on something a bit squishy, you would not be able to do that.

 

I also assume all the hoses have been plugged back in correctly e.g. the synchronising hoses and seeing you are in the US, you should have the hoses leading to the carbon cannister as well. Any decent leak in those will increase the idle speed and prevent the starter valves having any effect.

 

You did say that you replaced the inlet rubbers, are they all well seated/sealed? I had to swap out my thermostat and re-used the old rubbers and it took a bit to get them to reseal but a few heat cycles settled them down. 

 

You have replaced lots of bits trying to improve the idle but in reality the only thing to track down is an air leak, and that is only from the butterflies downwards; anything above those e.g. air filter, PAIR solenoids etc won't affect the intake vacuum. The one-way valve for the flapper, the purge valve for the cannister and the fuel pressure regulator are definitely important as is any hose that joins to them as they can all leak air below the butterflies. 

 

 

[rc24dk]

Is the idle settings depending on a temperature sensor or thermal switch? If so that could be something to look after.

[Brayden]

On 10/24/2024 at 6:47 PM, Terry said:

That is the non-adjustable throttle stop. If the throttle drum is hitting that screw firmly with a click then it seems you don't have anything caught up. I was wondering if during the process of checking the vacuum hoses for leaks, one had been mis-routed and was fouling a linkage. That would explain "when I roll the throttle back the other way the idle goes down but the idle is still sporadic but not as bad". Unless the throttle was being hung-up on something a bit squishy, you would not be able to do that.

 

I also assume all the hoses have been plugged back in correctly e.g. the synchronising hoses and seeing you are in the US, you should have the hoses leading to the carbon cannister as well. Any decent leak in those will increase the idle speed and prevent the starter valves having any effect.

 

You did say that you replaced the inlet rubbers, are they all well seated/sealed? I had to swap out my thermostat and re-used the old rubbers and it took a bit to get them to reseal but a few heat cycles settled them down. 

 

You have replaced lots of bits trying to improve the idle but in reality the only thing to track down is an air leak, and that is only from the butterflies downwards; anything above those e.g. air filter, PAIR solenoids etc won't affect the intake vacuum. The one-way valve for the flapper, the purge valve for the cannister and the fuel pressure regulator are definitely important as is any hose that joins to them as they can all leak air below the butterflies. 

 

 

Sorry for the late response but I’ve done so much digging around the throttle body it’s not even funny. Usually I can find small mistakes like a leak but I can’t seem to find it. I don’t believe the rubbers are the issue. I made sure they are tight and fitted properly. I have a smoke machine for testing purposes. Do you think I could hook up a smoke machine to a specific hose and find a leak? I’ve hooked it up before and smoke is coming back out through the butterflies? Are they partially cracked open for that or is it not supposed to happen? It would be great if I can find a leak with a smoke machine so just let me know! Thank you

[Terry]

3 hours ago, Brayden said:

Sorry for the late response but I’ve done so much digging around the throttle body it’s not even funny. Usually I can find small mistakes like a leak but I can’t seem to find it. I don’t believe the rubbers are the issue. I made sure they are tight and fitted properly. I have a smoke machine for testing purposes. Do you think I could hook up a smoke machine to a specific hose and find a leak? I’ve hooked it up before and smoke is coming back out through the butterflies? Are they partially cracked open for that or is it not supposed to happen? It would be great if I can find a leak with a smoke machine so just let me know! Thank you

I fully understand the frustration of repeatedly removing components to fault-find. I cleaned the carbs on my 1990 ST1100 about 7 times before I figured I had an electrical problem...

 

The butterflies should be sealed up tight with the thottle closed. If they don't seal, then the starter valves won't be having much of an affect on the idle speed. There should be a sealant in throttle bores to seal the butterflies. The pics below are from the Honda Common Service manual 2017 edition.

[Brayden]

1 hour ago, Terry said:

I fully understand the frustration of repeatedly removing components to fault-find. I cleaned the carbs on my 1990 ST1100 about 7 times before I figured I had an electrical problem...

 

The butterflies should be sealed up tight with the thottle closed. If they don't seal, then the starter valves won't be having much of an affect on the idle speed. There should be a sealant in throttle bores to seal the butterflies. The pics below are from the Honda Common Service manual 2017 edition.

Okay we are getting somewhere now I feel like. In that picture you sent it shows sealant on both sides. On my butterflies I only see sealant on one side and it’s really faded. Do you think I could reapply sealant or I have to get a new throttle body now?

[Terry]

Sorry but I don't know much about the sealant or whether it can be reapplied. My guess is that you might be better off buying a used TB at this point. Baboon Motor Parts in Netherlands has quite a few for sale at USD54ea , I've bought from them before and have been impressd with the delivery times (and I am a LONG way from Europe...). Good photos too, will allow you to compare what you have. BTW I think the sealant will only be obvious on one side of the butterfly until you flip the TB over and look at the underside).

 

I still maintain that you should not be able to roll the throttle further closed and have the idle drop.

 

e.g. https://www.baboon.eu/en/part/honda-vfr-800-fi-1998-2001-vfr800fi-rc46-throttle-body-assy-1999/000001400849