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creaky78
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OCT 26, 06:58 PM
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Can a faulty IAC sensor cause shifting problems with the TH125C?
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fierosound
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OCT 26, 08:00 PM
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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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My World of Wheels Winners (Click on links below)
3.4L Supercharged 87 GT and Super Duty 4 Indy #163
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phonedawgz
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OCT 27, 06:42 AM
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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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OCT 27, 05:44 PM
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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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OCT 28, 11:32 AM
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| quote | Originally posted by creaky78:
The tranny shifts late, about 3800 RPM. |
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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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OCT 28, 12:05 PM
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Thanks for the info fierosound, very helpful.
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theogre
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OCT 28, 01:29 PM
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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.------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave
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creaky78
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OCT 29, 07:28 AM
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Late shift in all gears or one/some?
Late shift in all gears.
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