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My car is running rich, and stinks of exhaust while at idle and my fuel economy is poor. However, when it's idling in neutral, the ROMs will get up to 1,500-2,000 and stay there.

I was trying to figure out my problem and covered one of intake ports going to the IACv from the manifold and the idle dropped and sat pretty comfortably.

So I assume that the ECU is thinking the IACV is closed but in fact it's wide open, and then the ECU is dumping more fuel into the engine to compensate?

Anyone have an IACV for sale?

What if I just plug the hole and drive without it?

Or when if I cover the hole but leave a smaller opening?
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Its EACV, not IACV.

Are you getting ECU code 14 and check engine light? This is what can happen when there is an EACV problem.

Its sounds probable that its the EACV but it could also be a problem with the fast idle control. Follow troubleshooting charts in the shop manual.

https://web.archive.org/web/2021061....co.uk/car/owner/media/manuals/PreludeManual/

If it is the EACV, take it off and flood it with carburetor cleaner and then let it sit for a few minutes before emptying the carb cleaner out, a few times over. This improved EACV problems for me, drastically. When you take off the injector wire sockets to get to the EACV, be sure the clips holding down the sockets don't fly off when you take them off.
 

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JDM 4th Gen Prelude 2.2 Vtec Turbo
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My experience is 4th gen specific, but the tech is the same. The IACV or EACV (whatever you want to call it) is attempting to rectify an issue with your idle speed, most likely you have an air leak in the system somewhere that it is trying to compensate for.

The systematic approach is to unplug the valve and run through the idle set procedure in the manual, if you can't set the idle low enough (to about 550rpm), you have an air leak you need to fix.
 
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