coolant bypass the throttle body??

I know a few of you guys have done this. I live in Texas so freezing is never a problem. THe last time I attempted to do a coolant bypass was when I first bought the car in 1995 (GSR w/out JRSC installed). The idle fluctuated like crazy so I swapped it back. I bypass by connecting the two coolant hoses that go through the throttle body with a straight pipe...I'm not sure that is the way it supposed to be done..I have no idea what the hell I was doing...and that is my question...can you bypass coolant to the throttle body without some crazy idling problem? How do you PROPERLY do a by-pass?

All your doing is bypassing the two small coolant lines (inlet/outlet) that goto the EVAC. I just used a "barb" from the hardware store, to hook booth hoses togather to make one.

I did not have any problems with my idle tho. Might try reseting your's, if you try it again.

-Ryan-

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"Noth'in like Induction...";)

88' CRX Si - JRSC @ 6psi
Endyn/Bosch FP, CarTech FMU, B&M CommandFlo
AutoMeter - Phantom FP, A/F, Boost gauges & pods, B&M FP Set
Eibach Pro-Control Bars, ARP Head Stud Kit, AEM Pads

If you are talking about the EICV (Electronic Idle Control Valve, or sometimes call an EACV for electronic air control valve) (not an EAVC) Then this is not correct!!!

You only bypass the inlet and outlets of the throttlebody! Bypassing the EICV will definately cause an idle problem! The only reason you bypass the TB is so that you are not heating up the incoming air charge! (for emissions and de-iceing).

Randy

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If your gonna do it, Do it right! Damn It!

[This message has been edited by Mochanic (edited May 24, 2001).]

agreed with mochanic...

coolant that goes to warm the TB is bypassed....so it's feeding coolant straight into what i know as mister IACV. Idle air control valve.

i've never heard of idle problems from the TB bypass before.

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96 gsr hitting 12s
90 hybrid hatch hitting 14s

I tried bypassing several different ways, the last and most logical was to bypass the TB by going from the head to the IACV and back. This still gave me a fluctuating idle. There is a thermovalve in the throttle body which apparently causes this. Someone told me that they opened up the water inlet of the TB and tightened this thermovalve and the problem went away but I was done screwing with it for such a miniscule mod.

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Bill Winters
Houston, TX
'94 bone stock GSR w/ home made CAI

"I will gladly pay you Tuesday for a supercharger today."

The thermo valve you are refering to is called the fast idle valve which simply raises the idle when the engine is cold.
You did have a good point!
You would have to remove the end cover of the fast idle valve and completely close this off by screwing in the valve so that the fake vacuum leak that is created by this valve can no longer work!

Randy


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If your gonna do it, Do it right! Damn It!
"Nothing feels as good as being Blown!"

[This message has been edited by Mochanic (edited May 24, 2001).]

Why would shutting off the coolant flow through the IACV (Intake Air Control Valve, EICV, EACV, why do they keep changing the name?) cause idle "problems" in warm climate? The coolant flow through there is only to preheat the air which it supplies to the engine and prevent it from icing. The signal from the ECT (Engine Coolant Temperature sensor), is what the ECU uses to determine what the target idle speed should be. With that value the ECU monitors RPM and increases or decreases the amount of air flowing through the IACV as necessary.

Some other random thoughts: The Fast Idle Thermo Valve works along with the IACV. The former supplies additional air which allows the IACV to operate over a narrower range than it would otherwise have to were it the only route for the extra air needed for fast idle. It already has to regulate idle air flow to account for accessory load. I can see how having a cold Fast Idle Thermo Valve might cause the IACV to close all the way, thereby taking control away from the ECU and allowing the RPM to change due to varying accessory load. Has anyone observed this? It makes closing the Fast Idle Thermo Valve, or at least closing it down somewhat, sound like it might be a good idea.

If you want to keep as much heat as possible from transferring from the coolant to everything downstream of the TB you have to stop coolant from flowing through both the Fast Idle Thermo Valve and the IACV.

As the weather is warming up, I'm going to try this mod. It seems likely that a hot throttle body contributes to the rising intake temps over time due to heat transfer from the intake air by the intake casting, blower, and intake manifold while cruising and idling. Those should be times when all of the downstream components get some cooling effect from the constant flow of unheated air, but the readings I took indicate that this isn't happening.

If it looks like a good idea, I'm going to implement as a shutoff valve in the coolant line. This way I can easily open or close it as necessary, obviously open in the Winter, etc.

[This message has been edited by rjaffey (edited May 24, 2001).]

I got it mixed-up, it's the EACV or IAC. Like everybody said, all it does is pre-heat the the TB.

My bad, for causing all the confusion..... http://www.hostboard.com/ubb/frown.gif AGAIN.

-Ryan-

"Why would shutting off the coolant flow through the IACV (Intake Air Control Valve, EICV, EACV, why do they keep changing the name?) cause idle "problems" in warm climate? The coolant flow through there is only to preheat the air which it supplies to the engine and prevent it from icing."

First of all you have a fast idle valve on the bottom of the throttle body and an EICV which is right behind the TB on the intake manifold. These are not the same thing which some people don't realize.
When doing the bypass you DO NOT bypass the EICV only the fast idle valve on the TB! The coolant flow through the fast idle valve is what we are trying to eliminate, because this is what heats the air flowing through the TB to keep the TB from icing, not the coolant flowing through the EICV.
A shutoff valve in the coolant line is a good idea for those of you in the colder climates, but remimber you only want to shut off the coolant to the fast idle valve, so this would require you to add a "T" before the coolant reaches the fast idle valve then on the branch going to the fast idle valve you would install a shutoff valve and another after the fast idle valve into another "T" so that you only isolate the fast idle valve itself! (With only one "T" you would allow coolant to backup up into the outging side of the fast idle valve and therefore defeat the purpose of the mod).

Randy

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If your gonna do it, Do it right! Damn It!
"Nothing feels as good as being Blown!"

Once again, I've got to ask WHY is there coolant flowing through the IACV-EACV-EICV?

The only reasons I can see it is that it prevents the IACV from icing and preheats the air that flows through it. A side effect is that heat also passes from the coolant into the side of the throttle body and the inlet casting just past it.

The coolant passing through the Fast Idle Thermo Valve serves three functions that I can see:

1) It operates the temperature dependant air bypass valve to provide more air when the coolant is cold so the IACV isn't forced to open beyond the range where it operates effectively to provide fast idle when the engine's cold.

2) It warms the throttle body from the bottom thereby warming the air that passes through it.

and

3) By warming the throttle body it also prevents icing.

The coolant passing through both of these components does heat the throttle body and therefore the intake air. More at idle and cruise than at WOT. How much? I'll post the numbers when I have them.

Anyhow, I see absolutely no reason why one shouldn't shut the coolant off to both of them if one is going to do it at all. Complicating the system with tee fittings seems totally unecessary and counterproductive. As for using two valves for total isolation, how much coolant is really going to back up through these components if the there's only one valve shutting off the flow from one end?

Am I overlooking something?

[This message has been edited by rjaffey (edited May 24, 2001).]

Bypassing the IAC keeps the spring inside the IAC from freezing in cold air climates and increases the spring's (k) resistance to the solenoid as coolant temps increases. But I think the coolant is mainly to keep icing off the spring/plunger setup. I've had the IACV bypassed for a couple of months now w/out any detrimental effects to drivability. But of course I live by the coast in California, where the weather seldomly reaches freezing. Combined w/ the TB bypass, the IAC coolant bypass reduces heatsoak considerably. Hondata has some comments about bypassing the TB and IAC coolant lines here: http://forums.clubsi.com/ubb/Forum12/HTML/005239.html http://forums.clubsi.com/ubb/Forum12/HTML/005386.html

Although Hondata is plugging there phenolic spacer it's still food for thought that he still bypasses the coolant line for the IAC and TB for reduced heat soak gains.


The two photos below show the internal workings of the IAC. It's basically a solenoid and spring combo w/ the ECU controlling it's duty cycle (basically like a solenoid regulating air flow for an electronic boost controller). The IAC is not only used for fast idle but also keeps the revs up when you let of the gas abruptly to prevent the engine from stalling out and increases air flow into the engine when power draining accessories are activated, i.e. headlights, power steering, AC...etc. The increased air flow helps the engine compensate for the increased load.
http://albums.photopoint.com/j/View?...463&Sequence=0

http://albums.photopoint.com/j/View?...467&Sequence=0

Here's the area that the coolant actually warms up.
http://albums.photopoint.com/j/View?...465&Sequence=0


I actually proposed this coolant bypass mod along w/ the TB bypass mod months ago but most weren't too clear on what I was attempting to do: http://www.hostboard.com/ubb/smile.gif http://www.hostboard.com/ubb/Forum40/HTML/004058.html

For a relatively easy mod, I can state that after running these two bypass modifications for the last couple of months that they indeed reduce intake charge and intake manifold heat soak times significantly. However, members that live in colder climates should we weary about this mod come winter time.

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Mods

[This message has been edited by zip (edited September 17, 2001).]

Since I have my engine bay cleaned out to get at the rear motor mount and put an oil cooler in, (intake, fuel line, throttle cable bracket, upper rad. hose, coolant line from head to TB are all removed currently), I believe I will try this mod. (Bypassing both TB and IACTV??!@VACTFE!#@$)

I do live in a cold place though. What will happen to me if I drive like this in, say, 40 degree humid weather (a typical nighttime except for late-June till early August)?

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Greg Holden
96 GSR, JSRC @10psi, All the Goodies!
Best 1/4 ==> 13.937 @ 101.41mph (at 6psi)
My JRSC Install Site

OK, here are some rather unscientific results:

I clamped off the coolant line running to the Fast Idle Thermo Valve and went driving (boosting perhaps 5% of the time) for an hour. This effectively stopped coolant from flowing through both valves.

I didn't have time to take before and after temperature measurements (I'll do that at some point and post results), but here are some observations and comments:

- The outside air temperature was about 55 degrees.

- After the coolant temperature gauge began to register above mininum, the idle speed began to drop a bit. After releasing the throttle the idle speed tended stick around 1500RPM for a few seconds and then drop to 1000RPM where it was not as stable as normal. I attribute these two things to what I proposed before, that the IACV is operating outside of it's normal range and therefore not having the charactoristics the ECU "expects". It might even be shutting all the way. This affects how well the ECU can accomodate changing accessory loads and implement the "dashpot" behavior Zip mentioned.

- After about 10 minutes of driving, I popped the hood and felt the blower, TB, Fast Idle Thermo Valve, IACV and coolant running from the IACV to the main water pipe; not the one I clamped off. The components and coolant line were still cool to the touch, though warmer than ambient. The other coolant lines were already hot.

- The idle stayed above normal for about 15 to 20 minutes.

- After about somewhere between 20 and 30 minutes (I can't tell exactly when as I was taking a non-stop cruise on Lake Shore Drive for about 10 minutes), the idle speed dropped to normal and stayed much more consistant with respect to accessory load. The dashpot behavior was normal as well. I popped the hood and felt component temps again. I found that everything had warmed up a bit, but the throttle body and air valves were nowhere near as hot as other coolant lines. They were just warm, perhaps 90-100F. The specs indicate that the Fast Idle Thermo Valve closes completely at 86F, so I conclude that after a period of time, it absorbed enough heat to close without coolant passing through it, though it might require the valve to be filled with coolant rather than air in order to maximize heat transfer from its casting into its "thermowax plunger". Another argument for a shutoff rather than completely disconnecting the Fast Idle Thermo Valve.

- The coolant line from the IACV to the main water pipe was about as warm as everything else, so I conclude that there's no need for two shutoff valves. I'll verify this when I take some before and after temperature readings.

- The idle would likely stay faster and more erratic than normal for a longer period if not indefinitely were the ambient air temp colder, because it would take longer for the Fast Idle Thermo Valve to absorb heat from surrounding components. It may never reach 86F if the surrounding air is too cold. Of course this is not a problem, as I'd open the shutoff valve and allow the coolant to flow normally were the outside temp much lower than it was last night.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>increases the spring's (k) resistance to the solenoid<HR></BLOCKQUOTE>

Zip, you're going to have to explain this one. http://www.hostboard.com/ubb/smile.gif

[This message has been edited by rjaffey (edited May 25, 2001).]

Rafe: So what you're saying is that one shutoff valve in the hose between the head and the TB will accomplish the goal and allow us cold weather guys to switch back to normal easily. Right?

Thanks,

Greg

Rjaffey, I think the SI and GSR coolant setups are different, since I'm positive that I've never seen the fast idle thermo valve you've mentioned. Here's a pict of an SI (typeR) big bore TB:

As you can see, there isn't an attachment for the fast idle valve you mentioned on your post.
http://albums.photopoint.com/j/View?...188&Sequence=0

The coolant merely just goes in and out of the TB and onto the IAC coolant ports I pictured above. From the IAC, the coolant lines end at the main water pipe. So to reiterate, the coolant flows from the head, to the TB, then to the IAC, and back to the main water pipe. I basically just connected the coolant hose from the head to the main water pipe, thereby effectively bypassing the IAC and TB from the coolant flow. Essentially, coolant flows freely among these components w/out a restriction imposed by any valve.

The spring resistance I mentioned is just an observation. Springs tend to increase in resistance as they warm up. I figure that Honda took this into account when designing the IAC operation at normal operating temps. As the coolant warms up the whole IAC assembly, the spring inside will tend to warm up since it's physically in contact w/ the IAC body. The IAC is left closed until extra air is needed by the engine. When the spring has reached its normal operating temps it "dampens" the plunger that the solenoid pulls against when the ECU sends the pulse signal to the IAC. Since the ECU sends pulse widths rather than a constant signal to the IAC, I think the spring helps keep the IAC open a tad longer.

When I bypassed the IAC I noticed that idle speed fluctuated just a little from normal (nothing drastic) since the spring wasn't aiding in keeping the IAC valve opened longer. Since Honda ECU's are pretty smart, http://www.hostboard.com/ubb/smile.gif the ECU would realize that the IAC wasn't being kept open w/ the preprogrammed pulse signal and it would instantly stabilize the idle w/ a new duty cycle. Just an observation.

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Mods

[This message has been edited by zip (edited September 17, 2001).]

Here's how my TB bypass expereince was:
I drive a JDM 4G Prelude VTEC.
At first, I only bypassed the coolant lines to the FITV and had a piece of thin metal plate to block it off from the TB. The hunting idle problem surfaced after a few days. So, I reconnected all the coolant lines back again and removed the metal plate. After reading about this problem in forums and some further suggestions, I went back at it again and this time, in addition to the FITV coolant lines and metal plate, I also bypassed the coolant lines to the IACV. What I ended up doing was simply connecting together the coolant fittings at the thermostat housing that was coolant suply/return point to the FITV and IACV. It's been almost a year and a half now since that mod and have never encountered the 'hunting idle problem'.

Zip,

Thanks for the clarification. Are you sure the IACV is receiving pulses rather than a constant signal?

Greg,

I think that's correct based on my testing last night. It's certainly worth trying out. It's clean, simple, and reverseable; the way I like all of my mods.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rjaffey:
Zip,

Thanks for the clarification. Are you sure the IACV is receiving pulses rather than a constant signal?

Greg,

I think that's correct based on my testing last night. It's certainly worth trying out. It's clean, simple, and reverseable; the way I like all of my mods.<HR></BLOCKQUOTE>

I'm sure the IAC receives pulses because it regulates incoming air to the motor which means it has to be pulse width controlled. The Helm also states that it's duty controlled hence pulses are used to control the solenoid.

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Mods

Guys, I've found that with any ACV (Air Control Valve) that has coolant lines into it is of the thermal wax variety...

What that means is if the valve is in a cold condition (enough to solidify wax) then your bypass will be open, regardless of weather you have manifold vacumm or not...

The coolant lines heat the wax, that in turn allows the manifold vacumm to close the bypass air, because the wax is now a liquid...

If you eliminate / bypass the coolant lines, than heat soak will be your only means of melting the wax...
(Hence what Rafe said, "it seems to take longer than what the ECU expects")...

If you just want to bypass a coolant line that runs under some throttle body's and just goes in and out you can...
Just don't be surprised if your cruise control doesn't seem to disengage in lower ambient temps... http://www.hostboard.com/ubb/cool.gif

As for bypassing

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Donny
Import Specialty Automotive
(253) 473-2606

Guys, I've found that with any ACV (Air Control Valve) that has coolant lines into it, is of the thermal wax variety...

What that means is if the valve is in a cold condition (enough to solidify wax) then your bypass will be open, regardless of weather you have manifold vacumm or not...

The coolant lines heat the wax, that in turn allows the manifold vacumm to close the bypass air, because the wax is now a liquid...

If you eliminate / bypass the coolant lines, than heat soak will be your only means of melting the wax...
(Hence what Rafe said, "it seems to take longer than what the ECU expects")...

If you just want to bypass a coolant line that runs under some throttle body's and just goes in and out you can...
Just don't be surprised if your cruise control doesn't seem to disengage in lower ambient temps... http://www.hostboard.com/ubb/cool.gif

As for bypassing

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Donny
Import Specialty Automotive
(253) 473-2606

Yes, that's what I'm talking about...erratic idle when performing the coolant bypass mod. I've done it in '95 but reverted back to stock form shortly afterwards...I don't know why others keep telling me idle will not be effected.

I went looking for part to make a shutoff valve in the coolant line the runs to the throttle body. The only valves small enough were meant for compression fittings onto hard piping. Perhaps this is what Rafe is trying to do with the OE hard lines he was looking for...

Anyway, I just cut the hose in two and plugged up the ends. I'll have to put a new hose in by September for colder weather.

The idle is, as expected, higher for longer when cold and then a bit erratic and lower after driving a while. This was in 50 degree weather.

Greg

This is a simple mod. From Home Depot (or equivalent) pick up the following:

- A 1/4" ball valve with 1/4" NPT threaded openings on each side. I found a nice small brass one with an SS ball and Teflon liner for just over $6.

- Two 1/4" NPT nipple to 3/8" or 5/16" barbed fitting. Short is better. I got ones with barbed ends that were about 3/4".

Now coat the threaded ends with TFE compound and thread them into the valve. Then just splice the valve into the coolant line between the intake manifold and the fitting right under the throttle body.

Now it's a snap to switch between hot and cold weather modes.

Havent been here in a while.

What I have done:

Took off screws from back of IACV (as shown above)

Ran the coolant line from the Water pipe to where the line originally came out of the FITV and into the intake manifold.

Had bad idle problems. FITV was the culprit. Didnt tighten it up, just took it out and put a block off plate in.

Ran the coolant line from thermostat to right below the distributor.

I have had zero problems and it is easily reversible. Took me all of 30 mins (minus making the block off plate) Saves some weight,too http://www.hostboard.com/ubb/wink.gif

Wish I had pics... need a digi cam.

BTW... fluctuating idle and a lightened flywheel is the most horrible thing I have ever experienced.

Pete

Random,

When you say you eliminated the "fast idle valve", do you mean you took out the thermo-valve underneath the front of the TB or the IAC on the firewall side of the intake?

Random got rid of the one below the T-body.

If you were to get rid of the IACV valve on the back of the intake in front of the firewall, you will throw a code 14 for IACV and it will idle high, shitty, and fast. Leave the IACV in and plugged up.

Pete

If you take out the throttle body (for ease of adjustment), take out the little plate that covers the fast idle valve..turn it all the way in to disable the valve. I live in Texas where it's hot hot hot all year long so it's not a problem here. In colder climate,I'm not sure.

Just by pass the coolant through the fast idle valve..do not by-pass the AVAIC (or whatever)...you'll this since the ECU is monitoring temperature here...

Did a coolant bypass the throttle body again...and completely eliminated the fast idle valve...solved my idle fluctuating for good...and cool the intake at the same time !

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Just by pass the coolant through the fast idle valve..do not by-pass the AVAIC (or whatever)...you'll this since the ECU is monitoring temperature here...<HR></BLOCKQUOTE>

I don't believe this is correct, at least not on the Hondas I've worked on. There's a separate sensor to measure coolant temp. The coolant flowing through the IACV is just to keep it from icing when the conditions are right for it. If you're trying to minimize heating of the throttle body, you don't want coolant flowing through the IACV either.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rjaffey:
I don't believe this is correct, at least not on the Hondas I've worked on. There's a separate sensor to measure coolant temp. The coolant flowing through the IACV is just to keep it from icing when the conditions are right for it. If you're trying to minimize heating of the throttle body, you don't want coolant flowing through the IACV either.<HR></BLOCKQUOTE>

I dont' know ... may be after some of you guys do the coolant by-pass (the IACV) and come back and tell us about it...But from what I have witnessed in the past, by passing the IACV will definately cause idle problem...

rjaffey,

Have you done this mod yet? Also, could you please post a simple diagram describing the plumbing of the home depot valve?

Thanks,
Charlie

Yes, I've done this mod and it works just fine.

The idle "problems", rather minor in my case; see my posts above, are only present when throttle body (and Fast Idle Thermo Valve) are below 86F or somewhere thereabouts. Above this temp the Fast Idle Thermo Valve is closed and out of the picture. My car's idle is completely normal above this temp. When it's a bit cooler, the idle is a bit high and slightly erratic until the Fast Idle Thermo Valve absorbs enough heat from it's surroundings. Although I haven't verified this, I think it's probably better to leave the Fast Idle Thermo Valve filled with coolant (my mod does this), as heat will transfer into the wax plunger faster than it would through air, thus shortening the period where the idle is faster and erratic.

The problem arises when the Fast Idle Thermo Valve is open, allowing more air flow, while the coolant temperature is aproaching or is at operating temperature. In this case the ECU is trying to reduce the idle speed via the IACV and the dynamic behavior of the engine is not matching what the ecu expects, there's effectively a closed loop operation between measured RPM and IACV duty cycle and having the Fast Idle Thermo Valve open when it shouldn't be as far as the ECU is concerned, throws idle control out of whack.

[This message has been edited by rjaffey (edited June 28, 2001).]

I also have cut and plugged the line from the head to the TB.

I don't notice any idle issues at all now that it's summer.

Greg