I've had my Fiero since 1999 and in that time it has always cold started at about 3000 rpm initially, then dropped as the car warmed up. Once the car has warmed up for about 3 minutes, it drops to about 1200 rpm and idles at 900 or so after warm and in Drive. In case I forgot to mention (and I did) '86 2m4, Duke, automatic.

First of all, there are no vacuum leaks on this motor (trust me) and there are no EGR issues as I don't have one (block off plate).

IAC is the same one I've had for the past five years or so and it's behaved the same all this time. TPS is good. Fuel pump replaced in the past few years and fuel filter is new.

Air filter new and the car uses very little oil.

Still, the high idle when cold concerns me. I was wondering if some kind of restriction for the IAC passage would lower the cold idle. It could be something that fits under the mounting bolt on the TBI near the IAC passage.

Does any of this make sense ? Even though I use synthetic oil, I hate hearing the engine race in the extreme cold we have here.

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That high idle is completely normal. My 86 auto idle exactly the way you describe. It probably does that to get the exhaust warmed up quickly for the thermac system. The engine management system on the early dukes was pretty low-tech so they have alot of odd operating characteristics that you won't find on a modern fuel injected engine.

You're probably right, but it still concerns me even though I've been dealing with this for the past 12 years.

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Well already you have proven you don't have a vacuum leak. If the engine idles at the correct rpm's warm (900) unless somehow your vacuum leak came and went with the engine being cold it couldn't be a vacuum leak. So yeah I agree.

I suppose you could block the vacuum passage. You need to think about it. If in any way that blockage could come loose, it's going directly into your engine. Also since the ECM has 3000 rpm as a target, it's going to try opening up the pintle even more. The restriction might only just make the ECM move the pintle even more and not actcually do what you want. You also might get a low idle SES light.

You could also have the ECM chip programmed so as to not idle so high.

Here a thought. Go to Radio Shack and buy a 1,000 ohm resistor and bridge it across the CTS sensor. When the engine is cold it will make the ECM think it's warmer. Now here's the kinda trick of it. Once the CTS sensor gets warm, the 1,000 ohm resistor bridged across it won't make much of a difference.

ie if the engine is at 120* the CTS would be at 1,000 ohms and the resistor would be 1,000 so bridged they would be tellign the engine 500 ohms aka 160*

Now if the engine is at 200 deg the CTS is at 225 ohms and that bridged with the 1,000 ohms would yeild 183 ohms or about 210*.

I don't know what size would work best, or if the resistor is going to wack out the ECM too much when cold to run right. Resistors cost $0.99 at Radio Shack. Might be worth a try. The higher the resistance the less it will alter the ECM. I don't think I'd try anything less than 1,000 ohms (1K ohm) This WILL make the engine run leaner however since the resistace at operating temps doesn't alter the perceived temp much I think you would be safe. Check your plugs. I would think being too lean at cold temps would be more of an issue than at warm temps.

Check your plugs when you do this to make sure your not getting your ECM to lean out the mixture too far.