Another 20v with idles problems

[Nexus09]

So my silvertop (closed airbox) is idling high. Around 2000-3000 hot or cold. I can force the throttles closed really tight and it will sometimes get down to 1500 but often ends up surging.

I have done my research and found that vacuum leaks are the number 1 cause. So I pressurized the system and no leaks.
I cleaned and got new lines for the Idle control valve and cleaned the crap out of the throttles.
I noticed when I had the airbox open and afm stuck open that it would idle around 1000, so maybe afm?
I started adjusting the afm (had never been touched before) and with the screw all the way out, it really just ran like crap and didn't change the idle that much so I reset it.
I re-tightened the throttle bracket springs with no results.

Only thing I have not tried is adjust the throttle bump stops.

I am missing something? Would love to get some of you guys ideas.

Thank you for reading.

[yoshimitsuspeed]

There should be a dashpot inbetween the ITBs underneath. It is pretty common for people to forget to hook this up and it will hold the throttles open a little bit without vacuum to close it all the way.

You definitely don't want to tamper with the AFM. Hopefully you marked where it originally was. It probably idles lower with the AFM propped open because the AFRs were so far out of whack (either too rich or too lean) that it caused the idle to drop.

It's always good to check the ignition timing because that can always effect idle speed but not by that much.
Once you have set ignition timing as close as you can and once you confirm the dashpot is hooked up you if you still have high idle you have too much air getting in somewhere so it will be up to you to find where.
If you don't have any vacuum leaks then you could make sure your ISC is set and working properly.
You could try capping that line off. If it still idles high you have too much air getting in somewhere else. If it idles right, too low or not at all then it's probably the idle circuit allowing too much air in and you just need to find out why.

[Nexus09]

There should be a dashpot inbetween the ITBs underneath. It is pretty common for people to forget to hook this up and it will hold the throttles open a little bit without vacuum to close it all the way.

You definitely don't want to tamper with the AFM. Hopefully you marked where it originally was. It probably idles lower with the AFM propped open because the AFRs were so far out of whack (either too rich or too lean) that it caused the idle to drop.

It's always good to check the ignition timing because that can always effect idle speed but not by that much.
Once you have set ignition timing as close as you can and once you confirm the dashpot is hooked up you if you still have high idle you have too much air getting in somewhere so it will be up to you to find where.
If you don't have any vacuum leaks then you could make sure your ISC is set and working properly.
You could try capping that line off. If it still idles high you have too much air getting in somewhere else. If it idles right, too low or not at all then it's probably the idle circuit allowing too much air in and you just need to find out why.

Thank you for the quick reply, I will try to look of that dashpot and check the ISC in the daylight tomorrow and let you know.

[jondee86]

There are a couple of things worth checking. It has been known for the
dashpot (throttle opener) to come loose on its adjustment. And if it ends
up too far forward, it can hold the throttles cracked open even if it is
correctly hooked up to vacuum. You need to ensure that when it retracts
on engine startup, it actually has clearance from the throttle arm.

The other thing, is that with quad throttles it takes hardly any opening
at all to raise the idle 1000 rpm or more. So you also need to check that
the throttle stops have not been messed with. From memory, there should
be a little dab of yellow paint on each screw to show that it was factory
set. The method of adjusting the throttle stops and linkages is quite
complicated, and if someone had messed with them, it would be easy
to get a couple of butterflys that did not close completely.

Last, each throttle has a air bleed screw that is only accessible on the
face of the throttlebody when the airbox is removed. These are factory
adjusted and set to balance the throttles at idle. They are not part of
any idle speed adjustment or tuning process, and should never need to
be touched during the life of the engine.

Cheers... jondee86

[phanist]

jondee

in the case of the 4 air bleed screw on each individual itb that you stated is factory setting and should never be mess with.. then how do we know if it been mess with or not?. is there a way to find out? after all i/we or most of us got the 20v used from importer.. unknown if any of this have been messed with..

[yoshimitsuspeed]

jondee

in the case of the 4 air bleed screw on each individual itb that you stated is factory setting and should never be mess with.. then how do we know if it been mess with or not?. is there a way to find out? after all i/we or most of us got the 20v used from importer.. unknown if any of this have been messed with..

I don't believe there is a way to know. I don't remember any paint or defining marks on those.
I also suspect it's something that is very unlikely to have been tampered with previously.

[Nexus09]

Ok I'm under the car now. All of the vacuum lines under the throttle are where they are suppose to be. Everything is plugged in and the yellow lines on the bump stops all line up. So the problem is unresolved.

I put about 7psi through the system and it holds it with no leaks.

The throttle were removed by me before I had the head rebuild. The only thing I did to them was clean the outside surface with a small wire brush and remove the two throttle brackets that's the throttle cable controls. Other than that, they have never been touched.

I can take pictures and videos if it will help, let me know.
Thanks for all the help.

[yoshimitsuspeed]

When it's idling make sure that dashpot is fully retracted and that all the butterfly actuators are sitting hard on the stops.

[phanist]

Check too see if your brake boost vacuum line are loose? And port that you may have gap off are loose? Clean your throttle make sure nothing is keeping the butterfly open when you release throttle.

[Nexus09]

When it's idling make sure that dashpot is fully retracted and that all the butterfly actuators are sitting hard on the stops.

Just to make sure, the dash pot is the part I between throttle #2 and #3, is gold/brass, had a rod coming outhouse the top that touches one of the throttle brackets when closed?

I feel like my throttles are not closing all the way. When it's idling high, I can push on the bracket holding the individual spring on each throttle and the idle will go down. But I'm just lost at this point.

[yoshimitsuspeed]

Exactly but when it's idling the vacuum should suck it in far enough that it's no longer touching that rod and is instead resting on the hard stops.

If vacuum does pull it in but not enough there should be an adjustment screw on there that you could turn in so it's not touching at idle.

[Nexus09]

Ok sorry this took so long, my days off are mon and tues.

I just necked the dash pot and replaced some hose clamps on the vacuum line for the brake system. I don't think they we leaking but I'm doing everything I can. The dash pot was fully retracted at idle.

Also, with the airbox off, I can plug the line from the airbox to the icv and the motor dies when throttles are closed. Is that what is suppose to happen?

Got it all back together, no change. Idles at 2100 warm.

[jondee86]

In theory, all the idle air should be entering the engine via the ISCV. And it
sounds as if it is, because you could stall the engine by blocking the ISCV.
You could try a fix used by some folk... inserting a plug with a fixed orifice
in the ISCV entry air pipe. Disconnect the ISCV from the airbox and use a
rubber bung with a small hole drilled thru the center. Start with 1/8" and
work your way up until you get the idle under 1000 rpm.

Personally, I think that this is a kludge, but if it brings your idle down to
an acceptable rpm, it might help out until you find the real cause of the
high idle.

Cheers... jondee86