tricky one for the duratec masters...

[Ronan]

For no reason one day, my IAC valve started to leak around the blanking plate, sucking air in. I replaced it, & the new one did that too.

Someone on here said the throttle hang fix can cause that to happen. I am running the svt t/b and checked the optimum sizes for the oriface. I have fitted these new sizes, and its still not working. If I fit an orifice with a hole too big, nasty throttle hang remains. If I go too small the IAC starts to suck again (and when the car is cold the idle is lumpy & it wants to cut out)

I've tried a few different sizes & either of the two effects above come into play.

My intake consists of a K&N ru3530, svt t/b, uim, & a greddy oil/air seperator (removed it made no difference).

Any ideas why this has suddenly happened? The car has been running fine for months with this setup.

Should I reset the ecu each time I try a different oriface plate?

Thanks in advance guys

 

[Ronan]

Ok, I think I got this one sorted before anyone replied! Trial and error.

I used a fitting, started with a small hole size, and gradually increased the size of the hole in the restrictor plate until the revs dropped down. Now it hangs for about 2 seconds at about 1300rpm when you come to a stop, but its hardly noticable.

What causes the throttle hang? Does it only happen on cars with a modified intake arrangement?

 

[98SVTC]

What causes the throttle hang? Does it only happen on cars with a modified intake arrangement?

From what I understand of emissions equipment, a certain amount of "TH" is built into the system in order to make sure the revs don't drop too quickly thus ensuring that all the fuel is burnt on deceleration. When the system begins to age a bit, it gets out of calibration and allows the hang time to increase. While the TH "fix" seems to work the best, it probably isn't emissions legal even though no one seems to have failed because of it. I used to remove the fix before smog testing but I don't anymore.

The practice of slowing down the drop in engine revs is nothing new. I recall dealing with early factory attempts at this back in the 70's when it was all mechanical. The preferred method at the time was a dashpot type of thing attached to the carburetor which would extend when the throttle was opened. When the throttle was closed, the center of the dashpot, now extended, would butt up against the throttle lever and slowly collapse away letting the throttle close. Of course, this bugged everyone and the non-approved fix was to adjust the dashpot back away from the throttle lever to allow the throttle to snap shut. Ah, the memories.
Karl

 

[Ronan]

Thanks for your reply. The car seems much happier now. I resetted the ECU too, and someone told me that the EECIV learns over time too?

Not sure if that part is true, but the idle is no longer a problem. I was thinking of getting a new 'chip', called the unichip. Its a specific map for a car, and it adjusts the fueling to ensure that you always have correct fueling, at all loads and rpm's.

I wonder would that chip effectly banish the throttle hang in the future if it were to return?