keysflier

Okay all you tuner gurus, here's what I've got:
Just purchased a 97 GT 4.6L (a measely 281 c.i. - God what were they thinking?!), 5-speed gear box, bone stock.

Fuel scheduling question: Is is normal for this little 281 to take several seconds to rev down when the clutch is depressed? Mine takes about two seconds to wind down to around 1,000 RPM, then another couple of seconds to wind down the rest of the way to a stock idle speed of around 750 RPM.

I suspect this may be deliberate on the part of Ford, it could be designed to preclude engine stalls from rapid deccelleration, and it might be programmed that way to assist in making shifts smoother. To me it is merely an annoyance and I want it to stop. Can a reprogram correct this, or am I looking at a pony of a different color?

Thanks one and all.

speedkills

Not sure if this works for 96-98 2v but here you go.

https://mustangforums.com/forum/4-6l...ging-rpms.html

sn95_331_GT_ yellow

^^
messes with your A/F at idle id steer clear...

best way is to correct it with a tune after you do some more upgrades to it

its annoying i know but just leave it be for now

FWIW mine does it too

uberstang1

Most of them are gonna to that to a point, I wouldnt even worry about it.

keysflier

Yeah I suspected as much. Darn thing behaves as if it's slinging a two ton flywheel.

cliffyk

The slow drop between shifts/revving the engine is normal--for emissions reduction. There is also a hang when coming to a stop while the car is still moving, this is to make sure there's more than sufficient power steering hydraulic pressure for the power assisted brakes.

The IAC restriction can make the revs drop faster between shifts however if too much restriction is used (too small a hole) the engine idle will be affected. This is not an AFR issue as the air through the IAC is metered by the MAF and the PCM is in closed loop mode at that time, it's just that the "too small" restriction cannot pass enough air.

The easiest way to implement it is to drill a hole in a 1/2" copper pipe cap and insert that into the IAC feed tube. I have found that 0.290" (a bit more than 9/32") works best. I was making these for some locals from aluminum rod--0.700" OD, 0.500" long, 0.290" bore:




There are settings in the tune that allow the IAC "dashpot" settings to be tweaked--I use a combination of the restrictor and adjustment of the tune's dashpot settings...

keysflier

As a follow-on, I couldn't stand leaving it alone. Went with Cliffyk's recommendation and inserted a 1/2-inch copper tubing cap with a 0.25-inch hole into the IAC feed tube. Problem solved. Thanks fellas!