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IAC sensor by creaky78
Started on: 10-26-2019 06:58 PM
Replies: 7 (228 views)
Last post by: creaky78 on 10-29-2019 07:28 AM
creaky78
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Report this Post10-26-2019 06:58 PM Click Here to See the Profile for creaky78Send a Private Message to creaky78Edit/Delete MessageReply w/QuoteDirect Link to This Post
Can a faulty IAC sensor cause shifting problems with the TH125C?
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fierosound
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Report this Post10-26-2019 08:00 PM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
A better description of what (V6 ?) engine/transmission are doing when shift problem occurs and what you're experiencing would help.
It may just be the TV cable that's misadjusted.

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phonedawgz
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Report this Post10-27-2019 06:42 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
The IAC is a motor that controls the position of a pintle that controls the idle speed. It is not a sensor.

Being a motor that controls idle speed it is highly unlikely to cause AT shifting issues.

[This message has been edited by phonedawgz (edited 10-27-2019).]

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creaky78
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Report this Post10-27-2019 05:44 PM Click Here to See the Profile for creaky78Send a Private Message to creaky78Edit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for the replies. Engine is a 2.8, transmission is a TH125C. The tranny shifts late, about 3800 RPM. I've been doing some reading, I'm thinking the governor might the culprit. The TV cable is properly adjusted.
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fierosound
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Report this Post10-28-2019 11:32 AM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by creaky78:

The tranny shifts late, about 3800 RPM.


RPM shift point will vary with throttle position (higher with heavy throttle).
I'm assuming it's going that high with light throttle when accelerating?

Diagnosis chart in Factory Service Manual - Hydraulic Diagnosis page 125-C3 indicates shift points in MPH not RPM.
You should check what your car is doing against that chart.

When I still had an automatic in my Indy, TV (Throttle Valve) cable adjustment made all the difference in shift points.
I could practically make the tranny shift "too soon" OR "too late" with it.

[This message has been edited by fierosound (edited 10-28-2019).]

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creaky78
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Report this Post10-28-2019 12:05 PM Click Here to See the Profile for creaky78Send a Private Message to creaky78Edit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for the info fierosound, very helpful.
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theogre
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Report this Post10-28-2019 01:29 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Late shift in all gears or one/some?

All can be crap in the governor. Can DIY but be very careful or can damage springs etc. Gov in part of VSS gearing.
If the trans was made for 4 cyl or another car heavier/lighter then Fiero may need governor weight/spring changes.
If you mod the TV cable to fit a different engine, very likely need pressure gauge on the trans to tell TV is adjusted right.

Car will have problems shifting w/ either or bolt parts have problems.

Some/one is other problems in valve body etc. and is a big job to fix parts inside. Worse, Many versions of TH125c/3T40 and many parts depend year of trans make.

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creaky78
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Report this Post10-29-2019 07:28 AM Click Here to See the Profile for creaky78Send a Private Message to creaky78Edit/Delete MessageReply w/QuoteDirect Link to This Post
Late shift in all gears or one/some?

Late shift in all gears.
.
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