Decel valve
09-08-2004, 03:25 PM
#11
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An easy way to verify would be to hook up a scanner and watch the IAC upon engine deceleration. My bet's on the IAC like Dave suggested.
If it is the IAC, it's all based on the ECU. It's probably a function of emissions. The way I see it, the IAC allows more air to bypass the shut throttle plate to make the engine decelerate more slowly, thus allowing the fuel cut to keep up with the engine deceleration. This way, less HC is spit into the exhaust, and likewise CO would decrease as well (provided everything else is functioning properly). Basically, it discourages an exhaust backfire (which is created from a fuel-rich exhaust gas combusting as soon as it mixes with fresh air that is sucked back into the exhaust pipe in between each pressure wave).
It's a bit of a stretch, but that's all I can come up with.
If it is the IAC, it's all based on the ECU. It's probably a function of emissions. The way I see it, the IAC allows more air to bypass the shut throttle plate to make the engine decelerate more slowly, thus allowing the fuel cut to keep up with the engine deceleration. This way, less HC is spit into the exhaust, and likewise CO would decrease as well (provided everything else is functioning properly). Basically, it discourages an exhaust backfire (which is created from a fuel-rich exhaust gas combusting as soon as it mixes with fresh air that is sucked back into the exhaust pipe in between each pressure wave).
It's a bit of a stretch, but that's all I can come up with.
09-08-2004, 03:45 PM
#12
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Originally Posted by xviper,Sep 8 2004, 03:02 PM
ps. Shifting rapidly with elevated rpm has never been an issue for me. In fact, in some instances, this is desirable (not letting off entirely on the gas). It does make the syncros work a bit harder but I've never found this to be damaging.
After owning 20 odd manual transmission cars, I just automatically (no pun intended) wait for the "feel" of the engine and transmission speeds matching before putting it gear under normal driving conditions. The only other car this happened on was (blush) a Pinto ( In my defense, post divorce). I fixed that by putting a pinprick through the rubber on the delay valve.
The whole thing is more annoying than problematic, and I'll learn to live with it. Other than that, I love the car
.
09-08-2004, 03:54 PM
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Originally Posted by FO2K,Sep 8 2004, 06:45 PM
I agree, and when I'm pushing it I always keep up.
After 20 I just automatically wait for the "feel" before putting it under. The only other this happened on was post divorce. I fixed that by putting a prick through the rubber on the valve.
The thing is more annoying than learn to love
After 20 I just automatically wait for the "feel" before putting it under. The only other this happened on was post divorce. I fixed that by putting a prick through the rubber on the valve.
The thing is more annoying than learn to love
09-08-2004, 04:05 PM
#15
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i mentioned this same characteristic 8 months ago on the first day i got my '04 - (edited by XV to keep the peace 
).
it was actually the first thing i mentioned to mindcore (who was with me when we picked up the car)
i find this "feature" to be something that i can't live without anymore.
upshifts are butter smooth as the motor almost senses the impending upshift and the revs are so close to where they naturally need to be.
with 23K on the car now, the delay has dissipated marginally (not sure why), but it's still there.
).it was actually the first thing i mentioned to mindcore (who was with me when we picked up the car)
i find this "feature" to be something that i can't live without anymore.
upshifts are butter smooth as the motor almost senses the impending upshift and the revs are so close to where they naturally need to be.
with 23K on the car now, the delay has dissipated marginally (not sure why), but it's still there.
09-08-2004, 04:50 PM
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[QUOTE=FO2K,Sep 8 2004, 01:45 PM]I see there was no resolution in the earlier thread. Odd that R11 has an 04 and didn't notice the delay. Like you said in your thread, it seems to be about half a second delay. PIA
09-09-2004, 10:11 AM
#20
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Flywheel weight is not it (affects accel but generally not decel). I can tell you on other vehicles that the decel was not affected by a super light flywheel.
My $.02? Stroke. I've noticed this problem on engines with a lot of stroke. I have not noticed it on the 00-03 S2k, at least not any I have driven. In fact, I thought the revs dropped to fast on my '01 except when racing. Then they are just about perfect.
An intake or vacuum leak can have the same effect but will usually affect idle quality quite obviously.
My $.02? Stroke. I've noticed this problem on engines with a lot of stroke. I have not noticed it on the 00-03 S2k, at least not any I have driven. In fact, I thought the revs dropped to fast on my '01 except when racing. Then they are just about perfect.
An intake or vacuum leak can have the same effect but will usually affect idle quality quite obviously.