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Throttle Hang Fix

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Throttle Hang Fix


This was spotted on the Contour forums, but the following information should apply to Mondeos as well...

All Contours/Mystiques equipped with the Duratec V6 experience this. It is likely part of the emissions control system.

Steve Westin put it this way:

My (incomplete) understanding is that it's pretty easy to tweak an engine for low emissions in steady-state operation; it's the transients that kill you. Because of this, engines have long had devices to hold the throttle open temporarily. I suspect that altering this will increase emissions. And I would expect that the program that decides when to keep the throttle open is complex enough that you won't be able to predict it. -- -Stephen H. Westin [email protected] The information and opinions in this message are mine, not Ford's.


Ray McNairy (RIP) developed a quick, reversible fix for this:

Turns out that "they all really do, do that." Sucks, but I concluded it is built into the smog calibration in the ECU as Furd always maintained . It's implemented by the air bypass valve position which is controlled by the ECU. What this valve does is bleed air from the rubber intake connector tube prior to the throttle body directly into the manifold. This effectively controls RPM under various conditions.

The "throttle hang" fix consists of installing a restrictor plate in the form of a 1/2" COPPER pipe cap inserted INSIDE the 3/4" rubber hose that supplies air to the bypass air valve. The cap is inserted at the manifold end of the hose and fits either the original or Mr. Moose hose. It also has a black tank, about the size of a fruit juice can, right under the throttle/CC cables. This plug has a hole drilled in it to provide sufficient air for idle RPM control but insufficient to maintain a RPM of in excess of 3K. The throttle drop is still slower than I would like but the "hang" is gone and that's a biggie.

For the SVT, or a car equipped with the SVT intake, the optimum hole size in the plug seems to be 3/16" or 7/32". For the stock intake, the best size seems to be 15/64". There are reports that the plug causes newer SVT's (E1) to lose power in mid-range RPM's, perhaps due to the newer IAC valves? The addition of the throttle hange restrictor plug has been reported to also fix the Mr. Moose (see related section on this page) issue without using the Ford Moose "bagpipe tube/hoses."

I removed the tank also but don't think this is necessary. I just pushed the plug into the 3/4" hose at the manifold end. For removal, a pair of pliers works well. The first time I started it, the engine "hunted" before stabilizing at 750RPM idle. Did this for when the lights were on and the AC. The ECU is learning the new position of the valve for maintaining the programmed RPM, which is normal. After two or three starts, it acts normal.

I would suggest getting several plugs-they're cheap-and trying different size holes. It needs to be just large enough to maintain cold or warm idle RPM's under worst case accessory loading. I assume this is cold day, cold start with the air on in defrost mode. Installing the plug is about a 3 min job once the hose is free and easily removable. Be sure it isn't cocked. Some WD-40 helps. It needs to be in far enough so that the hose fits on the nipple as per original. It will be too large to get into the mainfold.

Submitted by MONDYMANv6 (Originally posted on

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