Rev Hang Issue

95SvtCobra347 · Sep 30, 2017

My buddy has a 1994 gt that the rpm hangs between shifts anytime you rev past 2k before shifting. The car is a 5 speed. We have tried adjusting the IAC scew and the throttle stop screw cleaned the MAFS, new IAC, cleaned air temp sensor, new TPS, new throttle return spring. Kind of stuck here. I'm hoping the wealth of knowledge that this community posses can get us through this.

General karthief · Oct 1, 2017

you likely have not checked for codes, codes can be present without the check engine light on, go back to the 5.0 tech threads and click the tech/how to section, look for how to check for codes.

jozsefsz · Oct 3, 2017

You're on the right track with your adjustments, hanging throttle between shifts is typically the IAC staying open, the idle air bleed being too open, or the throttle plate hanging open. The pattern is that you're getting more air than you want when you chop the throttle closed.

A few questions - first, have you adjusted the idle air bleed? That's the hex-screw underneath the fuzzy fabric cover near the IAC on the throttle body. Second, have you checked for vacuum leaks or rotted hoses? That's another way to get more air than you want at idle. Third, does your car have a tune / chip? If there's something off in the tune, the IAC can be commanded to stay open more than you want.

If your car is all stock, and the vacuum lines are in good shape, I'd go through jrichker's 'Surging Throttle Checklist' available on this site to ensure your adjustments to the various screws have all been made properly. Not enough and you get surging at idle, too much adjustment and your idle will hang between shifts.

95SvtCobra347 · Oct 3, 2017

jozsefsz said:
You're on the right track with your adjustments, hanging throttle between shifts is typically the IAC staying open, the idle air bleed being too open, or the throttle plate hanging open. The pattern is that you're getting more air than you want when you chop the throttle closed.

A few questions - first, have you adjusted the idle air bleed? That's the hex-screw underneath the fuzzy fabric cover near the IAC on the throttle body. Second, have you checked for vacuum leaks or rotted hoses? That's another way to get more air than you want at idle. Third, does your car have a tune / chip? If there's something off in the tune, the IAC can be commanded to stay open more than you want.

If your car is all stock, and the vacuum lines are in good shape, I'd go through jrichker's 'Surging Throttle Checklist' available on this site to ensure your adjustments to the various screws have all been made properly. Not enough and you get surging at idle, too much adjustment and your idle will hang between shifts.

Thank you so much for the insight. The car is heavily modified but some critical info for internal components I am not sure of because the guy he bought it from couldn't tell me. He also told me the car had 11.5:1 compression and he ran it on pump gas which I know is a bunch of . He couldn't give me the cam specs either. It ran fine for the first couple months and just started tgus rev hang and it only does it when shifting gears.

Dan_Soprano · Oct 3, 2017

Check for vacuum leaks with starter fluid.

RioRed95Cobra · Oct 7, 2017

Did you reset the tps and such before or after you physically adjusted the throttle blade?

General karthief · Oct 8, 2017

Check tps after

jozsefsz · Oct 10, 2017

TPS checking isn't as important on the 94-95 as the Fox, provided you stay in a fairly wide voltage range that's acceptable to the computer as the starting point. If you haven't, the check engine light will let you know.

Mustang5L5 · Oct 11, 2017

jozsefsz said:
TPS checking isn't as important on the 94-95 as the Fox, provided you stay in a fairly wide voltage range that's acceptable to the computer as the starting point. If you haven't, the check engine light will let you know.

It's actually the same for the Fox. The actual range is fairly wide and you will get a code if out of range. The whole 0.9999 volt thing is misinformation.

Which brings me back to the question of running codes? Have you done it? Not all codes trip the CEL, and there are a few things can can possibly cause a hanging idle that would trip codes. Off the top of my head, a faulty VSS or even the NGS on top of the t-5 not being plugged in have been known to cause hanging idle issues.

General karthief · Oct 11, 2017

go through this checklist hanging/surging idle problems, you won't be replacing stuff at random and chasing your tail.
http://forums.stangnet.com/showthread.php?t=698148

revhead347 · Oct 27, 2017

Your friend's car is most likely normal. The computer has a rolling idle feature. When the car is moving, it holds the IAC open to keep the RPMs up for gear engagement between shifts. Either the engine has been modified which makes the RPM jump a little higher than necessary for gear changes, or the IAC is sticking a little bit. When you press in the clutch to change gears, the RPMs should stay where they were. If you press in the clutch and roll the car to a stop, the RPMS should drop to idle in abouit two seconds.

Kurt

jozsefsz · Oct 28, 2017

It depends on how long & how high it's hanging, whether or not it's considered normal. A little, yes, but on a modified car anything truly noticeable is abnormal. I've owned my '95 since '96 and when it was new and unmodified, it did this yes, but only by a few hundred RPM. Surging and stalling were more of a wear-problem that gradually occurred (started happening by around 50k). Once I modified it (tune etc.) it was a bigger problem until properly re-adjusted. The surging idle checklist above (if followed meticulously) will truly make sure it's in the normal range. When well-adjusted, again, "normal" is not noticeable. If you can feel it hanging, it will have the opposite effect of this feature (making shifts difficult and increasing clutch and engine wear). Kind of the opposite of rev-matching, and not a good thing.

Rev Hang Issue

95SvtCobra347

New Member

General karthief

wonder how much it would cost to ship you a pair

jozsefsz

95SvtCobra347

New Member

Dan_Soprano

RioRed95Cobra

Active Member

General karthief

wonder how much it would cost to ship you a pair

jozsefsz

Mustang5L5

That is…until I whipped out my Bissell

General karthief

wonder how much it would cost to ship you a pair

revhead347

Apparently my ex-husband made that mistake.

jozsefsz

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New Member

wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

wonder how much it would cost to ship you a pair

Apparently my ex-husband made that mistake.

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