The FIAV (Fast Idle Air Valve) seems to be misunderstood, so I thought I'd make an informative post for the archives.
The FIAV is located in the lower half of the throttle body on the right-hand side. It's purpose is to provide additional air when the engine is cold to increase the idle speed and therefore warm up the engine faster. The FIAV is the reason (the only reason) that coolant flows through the throttle body. The way it works is that the coolant flows around a small wax pellet. As the coolant heats up, the wax pellet melts and the valve closes, thus slowly decreasing the amount of extra air let into your engine.
If you took the upper and lower halves of the throttle body apart, it would look like the following picture. Please note that if you do decide to take the upper and lower halves apart, take great care with the 5 phillips-head screws - they are torqued in quite tightly and are easy to strip out.
![Image]()
The inlet and outlet on the left side allows the ISC to function, the inlet and outlet on the right side allows the FIAV to function. Coolant flows through the area in the middle.
I wanted to re-route my coolant lines, and if you choose to do this, you should really block off the FIAV. The following is a short explanation of how I did it. This is not necessarily the only or even the best way to do it, and I will try to explain other options as I go along.
The following picture is a top down view of the lower half of the throttle body. To block off the FIAV, we want to block off either the inlet or the outlet so that air will not flow through it. The easy way to do it (the way most people do it) is to use JBWeld or RTV to seal the outlet for the FIAV. The inlet is nearly impossible to seal, as both the ISC and the FIAV share an inlet opening.
![Image]()
Of course, I've never been one to do things the easy way, so I instead fabricated a plate to sandwich between the two halves of the throttle body. Here is a picture - please note that I cleaned it up and smoothed it out more after I took this picture.
![Image]()
For the record, I think making a plate like this is overkill, and the JBWeld/RTV fix would probably work just as well. As you can see, I've made inlet and outlet openings for the ISC, but blocked off the outlet (and part of the inlet) for the FIAV.
Then, I just sandwiched the plate between the two halves, and made generous use of RTV to ensure a good seal. The finished product looks like this:
![Image]()
Of course, you want to make sure that you re-route the coolant lines. There's a few different configurations of hoses and fittings, but here's how I did it:
![Image]()
Well, after all that, my FIAV is blocked off. I've eliminated a potential vacuum leak, I keep my throttle body marginally cooler, and my car doesn't rev quite as high on startup.
This is probably not a good idea if you live somewhere that is cold, as you may have to ride the gas pedal until the car gets up to temperature.
Hopefully this information helps someone.
For the archives: idle surge fast bounce fiav leak 400 500 600 700 1200 1300 1400 1500
The FIAV is located in the lower half of the throttle body on the right-hand side. It's purpose is to provide additional air when the engine is cold to increase the idle speed and therefore warm up the engine faster. The FIAV is the reason (the only reason) that coolant flows through the throttle body. The way it works is that the coolant flows around a small wax pellet. As the coolant heats up, the wax pellet melts and the valve closes, thus slowly decreasing the amount of extra air let into your engine.
If you took the upper and lower halves of the throttle body apart, it would look like the following picture. Please note that if you do decide to take the upper and lower halves apart, take great care with the 5 phillips-head screws - they are torqued in quite tightly and are easy to strip out.
The inlet and outlet on the left side allows the ISC to function, the inlet and outlet on the right side allows the FIAV to function. Coolant flows through the area in the middle.
I wanted to re-route my coolant lines, and if you choose to do this, you should really block off the FIAV. The following is a short explanation of how I did it. This is not necessarily the only or even the best way to do it, and I will try to explain other options as I go along.
The following picture is a top down view of the lower half of the throttle body. To block off the FIAV, we want to block off either the inlet or the outlet so that air will not flow through it. The easy way to do it (the way most people do it) is to use JBWeld or RTV to seal the outlet for the FIAV. The inlet is nearly impossible to seal, as both the ISC and the FIAV share an inlet opening.
Of course, I've never been one to do things the easy way, so I instead fabricated a plate to sandwich between the two halves of the throttle body. Here is a picture - please note that I cleaned it up and smoothed it out more after I took this picture.
For the record, I think making a plate like this is overkill, and the JBWeld/RTV fix would probably work just as well. As you can see, I've made inlet and outlet openings for the ISC, but blocked off the outlet (and part of the inlet) for the FIAV.
Then, I just sandwiched the plate between the two halves, and made generous use of RTV to ensure a good seal. The finished product looks like this:
Of course, you want to make sure that you re-route the coolant lines. There's a few different configurations of hoses and fittings, but here's how I did it:
Well, after all that, my FIAV is blocked off. I've eliminated a potential vacuum leak, I keep my throttle body marginally cooler, and my car doesn't rev quite as high on startup.
This is probably not a good idea if you live somewhere that is cold, as you may have to ride the gas pedal until the car gets up to temperature.
Hopefully this information helps someone.
For the archives: idle surge fast bounce fiav leak 400 500 600 700 1200 1300 1400 1500
