As far as i am aware the Ericks T/B's dont have the water coolant passages you mention, certainly mine doesnt and with reference to the IAC I have also bypassed the IAC with no adverse affects to my idle.

I must state though that the car is not used in "Winter time"

 

Thank you for posting this - very pertinent information.
Bunji lives in Vancouver and right now, it is getting cooler and it's always very humid there. With this combination of cool and humidity, I think that with NO coolant to warm up the TB and the IAC mechanism, certain driving scenarios are more likely to produce this sort of behavior. I also believe that as the temps get to Vancouver's winter averages of being in the 40's and 50's, that Bunji will find the car having this weird high idle more and more. Unless there are other extenuating circumstances, you're going to have to live with it.

ps. At the very least, try to run the coolant lines into the IAC system.

 

Time for another psychic diagnosis.

I think your problems with the fast idle and high idle on overrun is caused by a poorly adjusted throttle stop, leaky throttle plate or air leak.

Normally, when setting up a throttle body, the idle motor is disabled and the throttle stop adjusted so the engine idles very low (600-700rpm). This sets the base idle air flow. The idle motor is then reconnected and will provide additional air to control the idle. Normally an idle motor will have a control range of 3-400rpm which is enough to control idle with a cold motor/cold oil.

In your case it sounds like the throttle plate is passing too much air at the idle stop. The idle valve will be fully closed as it cannot reduce the idle enough to get to 900rpm. The idle valve can only provide additional air to increase the idle. If the base idle is too high the idle valve cannot reduce the air flow.

Now what about the very high idle on overrun ( car at > 0 speed). Most cars have an overrun mode which increases the idle on overrun for several reasons. This includes,
1. making the car easier to drive at low throttle openings so the car isnt jerky off zero throttle
2. Stopping the engine stalling when returning to idle.
3. Better emissions control on overrun. The cats need air/fuel passing through them to work optimally. If there is no overrun mixture flow its very hard to meter the correct fuel to keep near lamda 1.

Generally the overrun mode opens the idle air valve fully during the overrun period. In your case the idle is already too high with too much air passing past the throttle plate. In overrun mode a fully open idle valve is giving you way to much air and resulting in a very high overrun idle.

I would suggest getting someone to unplug the idle motor on a stock F20C when warmed up and seeing what the base idle speed is. You can then disconnect the idle motor on your engine and adjust the base idle to match this. Make sure the throttle plate isnt hard against the throttle housing or it will eat into the aluminium. If you cannot get the idle low enough without the throttle plate graunching into the housing you either have to put up with it, or get a higher tolerance throttle body. I would suggest trying a base idle of 600-700rpm as a starting point.

This may fix itself after time as you normally get a black residue build up on the throttle body which helps seal the plate better. Some manufacturers use a sealing "paint" on the inside of the throttle body to assist with sealing.

Hope this helps.

Chris Barry

 

Another thought inspired by Chris' post.

Have your ever adjusted you throttle cable? (Just reread your original post and see you have the Erik's TB so, yes) I know some guys took out the slack for more immediate throttle response. Do this on a hot day (when things expand) and on a cold day (things contract) and you will have aslightly open throttle.

 

wow....I'm now being overwhelmed with imformation and potential solutions. Thanks for all the inputs.......I'm very interested with chris's input. I will bring this attention up to the mechanic sometime next week. I will post the findings and results as soon as I get the problem fixed. Thanks all!!!