Issue: Cold Start and Idle rough

New to this forum, im pretty out of ideas on the VFR. Its an 02, with all the standard mods flapper box, PAIR, O2 delete etc. Its got an older PCIII and a vincent exhaust. Ive had the bike a little while now, and its never ran quite right. Originally it would run like shit from idle - 2500rpm, and when you pulled in the clutch the RPM would stick at 4k. After ripping the throttle bodies off I realized that the idle adjuster had been maxed out and lodged, so the idle was set alll the way up (even higher than the cold start wax valve).

So, recently I replaced all the vacuum lines, replaced the wax valve, cleaned and synced the idle valves, had my fuel injectors cleaned and synced, checked for vacuum leaks by spraying carb cleaner down there etc. Everything should be tip top as far as the intake system goes. However here is my issue.

On cold start, it idles at 1000rpm, which makes it really hard to start. Once its warm it sits at 1000rpm, I can only adjust the idle via the adjuster from 800rpm to 1000rpm. I can continue to open the idle valves more and more but the RPM doesn't increase. Its almost like whatever controls the fuel mixture for the idle circuit isn't working. It still runs like crap up to about 2500rpm, which if its running lean because its not getting the fuel it needs, could be why. What controls the fuel at idle, is it the MAP? Doesn't seem like that would be it since you leave that hooked up during the sync (and you are suppose to be able to change idle, which i synced at 1000 because thats all it would do) and its not feeling the vacuum changes.

Anyone got any advice?

(This is also posed on VFRDisussion)

 

Please clarify by what you mean that it is not feeling the vacuum gauges. Did they register vacuum? What is the reading, approximately 20 inches Hg?

Is one of the starter valves fixed as it should be from the factory?

Aside from the idle are you riding it? It runs fine with throttle?

 

What i ment by that was it seems like even though the idle valves are pulling more vacuum something in the idle circuit doesn't seem to be reading it. During the sync yes the 4th idle valve is locked and that what i synced to, my gauge showed just over 6 vacuum inches

 

Someone else here has to confirm the raw numbers and the scale. I thought typical vacuum is 20 in. Hg.

 

A normal intake vacuum is about 10" Hg or 25 cm. 4 inches is very low and suggests that there's a big intake leak in there somewhere.

 

I tore the entire thing back off and apart last night, and ensure it was all hooked up correct. I re-synced and it was at 5.5", none of them required much differentiation, so its odd that something would be wrong with every single intake. I sprayed carb cleaner to see if it would dog or raise the RPM to check for a leak and didn't see any change.

 

Yes I got the unit wrong (thanks Cadbury!) My number was cm, and inches = cm*2.54. Your measurement cannot deviate by a factor of two from these numbers without there being a problem. However, check your gauge, is it in PSI? Your numbers would be dead on in PSI units! Then we can move on to perhaps the fueling that you suspect.

The coolant temperature sensor feeds back to the ECU to alter the mixture based on temperature. Does the idle change with engine temperature or it is always terrible?

Test the Fuel pressure regulator? Maybe the engine is drowning at idle?

 

Here is a picture of the gauge, it shows inch pounds for vacuum and foot points for pressure. Full disclosure this is a Chinese gauge so it could be off. I've used it many times to sync things but never payed attention to the actual reading.

On cold start it doesn't idle up, I just tired it and it started at about 900 rpm and as it warmed up then the idle went up to about 1200.


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The one thing that should make the idle high is the wax unit. Can you see whether the length of the unit is changing as it should from cold to hot? When cold, I understand it should be holding the starter valves open, and when cold it shouldn't be contacting the SV plate at all, the SV plate should only be resting on the idle screw.

With the PAIR mod, are you confident the PAIR port on the airbox is plugged?

 

Great photo thanks. Yes, the vacuum gauge that rotates counter-clockwise from the needle is not psi or inch pounds but is inches of mercury on the outside and mm of mercury on the inside. These dials still read as though they are measuring the height of a column of mercury in a fluid gauge. It should show "Hg" (mercury) for clarity but doesn't.

So vacuum is low, listen to Cadbury to find where pressure is going.

 

I am 100% confident the wax valve is working correct, pulling back on the SV plate then when warm letting go till it sits on the idle adjuster. The idle adjuster works as well, and all idle valves move freely. That was the first issue I had so I have been through all of those, cleaned, replaced etc. all vacuum lines replaced as well.

The PAIR port has a cap over it with a hose clamp. The entire system was gutted prior to my owning. I'll take a second look at the cap and make sure there isn't a rip or other issue letting air get by.

 

When all is said and done with air and fuel, that may leave a timing problem. I think that retarded timing would reduce idle vacuum. Do you know if the valves were adjusted on this engine?

 

I don't know about the valves, it's got 40k miles so it could be. Can the timing be checked on these with a timing gun?

 

I think Knight is referring to checking that the cams are correctly set relative to the crank. You need to pull the cam covers off and check the marks on the cam gear and the corresponding mark on the flywheel. I guess it is not impossible for the timing to be one tooth out and the engine would run without valve interference but might not run too well.

Coming back to the starter valves, what work was done on those? My thinking is that they don't seem to be functioning as expected in terms of the idle speed. Maybe (and I'm just throwing this out there) the ports that the SV's sit in are blocked so the SV's don't do their thing ptoperly.

Also (and again just a suggestion) maybe one of your vacuum lines isn't sealed properly or is not connected to the right device. I've left off the hose to the MAP sensor in the past, and in addition to the leaky sound the bike was not happy on re-start.

 

I recall reading that an owner caught this problem with their very first valve check, aka the bike came that way, if we can believe that! Must have been the one engine that Honda mis-configured.

 

If the timing is off by a tooth, I should be able to see that with a timing light as well, without having to pull the valve covers. Would rather not have to order new gaskets if I dont have to, and its just easier. On the flip side, might not be a bad idea to take off at least one side and take a look in there and make sure everything looks ok. It'll likely be a couple days before I can get this done, but i'll give it a go. Maybe i'll take a stab at checking valve clearance (on the non vtec valves at least) while im in there. Im assuming since the vtech valves dont engage until vtech kicks in, they shouldn't be my issue and maybe i can skip that headache.

I pulled the throttle body assembly, pulled the idle valves, blew out the passages with a compressor, wiped off the idle valves themselves, replaced all vacuum tubing with new (one line at a time to ensure I didn't mix up what goes where), put in a new wax unit, had all of my injectors cleaned and rebuilt, put it all back together. The accuation of the idle valves work perfect, they dont stick and they slide with the CV as they should.

This issue has been around since I bought it, so its not something that I did, but could be something I didn't do. Maybe I should take the throttle bodies back off (ugh) and make sure that they are all hooked up correctly. I know I put them on how they came off, but I dont know for sure that they came off the correct locations. They seemed logical looking at them, but thats not for sure. I didn't check the passages themselves, but air seemed to blow through everything ok. Since it effects all 4 cylinders, it just seems like it would have to be something a level higher thats causing vacuum to escape, not at an individual cylinder level. Maybe there is a hose completely missing that I also missed the nipple for, or something is unhooked down the line. I know the map is hooked up, and its not hooked up to vacuum when doing the sync anyways.

I would hope that at 40k someone would have caught this, but you never know. I'll be giving it a check

So, my next steps, take the throttle bodies back off and 3x check them. Take off a valve cover and make sure timing isn't off a tooth.


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I followed the shop manual for the sync. Lets take a step back and make sure i didn't screw that up.

1. Took off the airbox
2. Unhooked the MAP and the air temp sensor from the airbox
3. Took the MAP off of the airbox
4. My PAIR is already unhooked and plugged
5. Unhooked the 4 vacuum lines that go into the 5 way, plugged each of them into my gauge
6. Hooked back up the MAP, plugged it into the wiring harness, plugged it into the vacuum line (at this point there is nothing else on that as it plugs into the 5 way thats all unhooked).
7. Started the bike, let it warm up so that the CV plate is off of the wax valve, attempted to set idle to 1200, checked vacuum

 

I watched this video here to ensure what I was doing was correct, people seem to agree this is a good video. Looking at his gauge, he is only pulling maybe 7in vacuum. I was pulling about 6. He also doesn't hook the MAP back up to the harness like the manual says. However I couldn't imagine that would really mess up the overall vacuum reading.

[video]https://youtu.be/1sj33NXnm1c?t=7m24s[/video]

Thoughts? Im going to go out and run the sync again, and i'll take a pic of my gauge reading while doing it.

 

More food for though, I only had about 15min to screw with it, but I do have a Cali bike, so I checked the purge valve which was fine. But i also unhooked it while the bike was Ideling and the rpm didn't even hiccup. The Evap circuit taps into every cylinder just like the map sensor, so by pulling the vacuum off the valve it opened every circuit. I would have expected something to happen. I didn't have my gauges hooked up to see if it dropped the overall vacuum, but I hope to do that soon. Honesty I don't know if this test supports or hinders the hypothesis that we are chasing a vacuum leak or not. I can see it both ways.


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I don't have a CA bike, but I know if I disconnect one of the vacuum hoses I get a change in idle speed and a change in noise. I think you are onto something there.