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Does anybody know what purpose the coolant is for on the intake air control valve (IAC)? I've been running w/out the TB coolant since the JRSC install and I would like to bypass the IAC valve also, do you think it's feasible? BTW, I live in Cali. so the temps never reach freezing.
I'm assuming you're talking about the IAC valve on the TB? The coolant tells the ecu to open or close the valve depending on the coolant's temperature. It works like a fast idle valve. The colder the coolant, the more the valve opens to let in air (the little hole in the bore of the TB) that bypasses the throttle plate. And vice versa as the coolant gets warmer.
Why would you want to bypass this valve?
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99 Civic DX Hatchback, JRSC + FP, Eibach Pro Kit, ST Sway Bars, Borbet Type F's, Yok A520's 205/45-16's
I was just contemplating on this mod because every little mod counts when you lower the TB temps. Since the IAC, on the Si anyway, is connected next to the TB, I'm assuming it would lower intake manifold temps if I disconnected the coolant flow. The IAC valve on the Helm manual looks as if the coolant just does the same function as the TB coolant passages. The diagram looks as if the coolant passage is used to keep the spring on the solenoid driven IAC to keep it from freezing (akin to the TB sticking in cold weather). It seems the ECU controls the duty cycle on the IAC solenoid to maintain fast idle and idle speed in relation to engine coolant temps. So by directly bypassing the TB and IAC, wouldn't I lower the intake temps at the TB considerably, or at least maginally? I'm going to try this mod out and see if it helps in any performance gains.
Zip,
The coolant through the fast idle valve under the throttle body serves to prevent icing and as a signal for the fast idle valve, which determines how much extra air to feed the engine when it's cold. The coolant through the IAC valve next to the throttle body is just to keep the IAC valve from icing.
Zip, did you see my last post about the new Jaz setup I had in mind? What do you think?
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Fred G.
'97 Civic EX supercharged http://www.geocities.com/motorcity/track/4059
Beech 1900D driver...2,558 shp, 10,000+ ft./lbs. tq., top speed 331 mph :)
Rjaffey: your saying that the IAC has a temp probe or some kind of bi-metal that regulates the air flow w/ respect to engine coolant that's flowing through the unit? I thought the ECU drives the solenoid w/ respect to the engine coolant signal from the water temp probe. If not the icing problem is not a concern since I live in Cali and it never reaches freezing temps here anyway.
MouhadIb: what does the problem have to do w/ the coolant passages. I think the problem your experiencing is that the solenoid is not working properly or that the ECU can't regulate a proper pulse width to maintain idle.
Zip,
I'm sorry if I was unclear. The Fast Idle Thermo valve located under the throttle body is purely mechanical and responds to coolant temperature. It's job is to provide more air flow, bypassing the throttle plate, when the engine is cold for faster idle. As the coolant heats up, the Fast Idle Thermo valve closes down. It's function is very similar to that of a choke on a carburator. The coolant passing through the Fast Idle Thermo valve also warms the throttle body itself to prevent icing under certain conditions.
The Idle Air Control valve controls additional airflow bypassing the throttle body. It is controlled by the ECU. The coolant temp, the A/C compressor load, and various other inputs determine how much air is required to maintain consistant idle speed. The ECU also uses the Idle Air Control valve to maintain a slightly higher idle speed when the coolant is cold. The coolant passing through the Idle Air Control valve body is to prevent icing under certain conditions.
Remember, air temps drop as pressure drops. Even though the intake air may be above freezing, it's possible for passages through which the air flows to ice up under the right conditions.
zip,
Here is something to consider. My IAC control valve is not working right now and the CEL has been on. I get a code 14 which is the IAC valve. The idle on the car is soooo low that I have to accelerate the car in order to get cold air from the AC. If I don't the idle is so low that the compressor can't turn on. I can hear it clicking and clicking. Also the car stalls when I coast to a stop with the AC on. Just something for you to consider about the functions of the IAC valve.
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It take a Nation of Millions to hold Us Back!!!
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[This message has been edited by MouhadIb (edited September 13, 2000).]
I've decided that I'm going to bypass the coolant from the IAC to futher reduce intake heating near the TB area. I've already bypassed the TB coolant since the SC was installed. I'm hoping that eliminating coolant from the TB and IAC will reduce the heat on the intake charge. I've looked at the diagrams of the IAC on the B16 and it doesn't use the bimetal spring to compensate for coolant temps. However, the D engines use the bimetal spring, so bypassing the coolant may not be adviseable for them.
http://albums.photopoint.com/j/View?...nce=0&res=high
The lower right ports is where the coolant flows through the IAC.
http://albums.photopoint.com/j/View?...nce=0&res=high
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Mods
I bypassed my coolant at the TB awhile back. My idle fluctuated from .5-2K constantly with that set up so I went back to the stock configuration. Something you might want to keep in my before you do the bypass.