1996 Manual Transmission ECU

nfbeckman

Well-known member
Dec 10, 2013
110
14
Memphis,TN
I am curious about what caused your idle issues. Was your ECU replaced or was it something else? Do you know the revision level of your ECU?
When I bought the truck it did this. When you crank it it would idle up like a normal cold car. 1100 rpms. But as soon as you start driving the rpms would just stick wherever you had it when you shifted. come to a complete stop and they would come back down.
 

terryjm1

Well-known member
Jan 23, 2011
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Couldn’t figure out how to attach a pic to a PM. Here is the ECU out of my 96 5 speed parts D1. The tune it shows is 9637, which would make it an auto box tune for 96.image.jpg
 
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efacewin

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Jun 11, 2017
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I am learning as this thread progresses.

One thing I am now convinced of is that setting the software switch from automatic to manual will not change the “tune level”. I am fairly convinced the 5-speed ECU needs an eprom that matches one of the manual tune levels. (Later ones than originally installed in a vehicle should be fine).

I’m now exploring if an eprom can be cloned.
 

efacewin

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Jun 11, 2017
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Really? Now I need to go look at mine and see what it says because I still have some funky throttle issues at low speed
As you probably know, some of those idle issues could be vacuum related. If you unplug your IAC (stepper motor) while it is running and leave it unplugged, any erratic idling is not related to the ECU. This is how I run mine except in the summer when I need to use the air conditioner. PS. it is important to unplug it while engine is running. This is necessary since the ECU opens the stepper motor at shutdown in anticipation to the next start.
 

nfbeckman

Well-known member
Dec 10, 2013
110
14
Memphis,TN
As you probably know, some of those idle issues could be vacuum related. If you unplug your IAC (stepper motor) while it is running and leave it unplugged, any erratic idling is not related to the ECU. This is how I run mine except in the summer when I need to use the air conditioner. PS. it is important to unplug it while engine is running. This is necessary since the ECU opens the stepper motor at shutdown in anticipation to the next start.
Mine is really weird. It all related to if it’s rolling or stationary. I ended up just adding a kill switch on the vehicle speed sensor wire and it completely eliminated the problem. The idle would jump up and down when I was trail riding in low range. This kill switch made the throttle smooth as silk.
 

efacewin

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Jun 11, 2017
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Mine is really weird. It all related to if it’s rolling or stationary. I ended up just adding a kill switch on the vehicle speed sensor wire and it completely eliminated the problem. The idle would jump up and down when I was trail riding in low range. This kill switch made the throttle smooth as silk.
Interesting. Unplugging the stepper motor (IAC) is a similar solution. It is the only way the ECU can directly adjust the idle speed.
 

nfbeckman

Well-known member
Dec 10, 2013
110
14
Memphis,TN
Interesting. Unplugging the stepper motor (IAC) is a similar solution. It is the only way the ECU can directly adjust the idle speed.
Not completely, the computer can still adjust the timing changing the rpms a few 100 in either direction. I tried unplugging the stepper motor when I was having erratic engine speed fluctuations when in low range on my last camping trip and it helped but the engine speed still varied at low speed without me changing my pedal position. Unplugging the VSS completely smoothed things out. I have no idea why but the computer was advancing the timing as soon as the vehicle started to move. Reguardless of if I had my foot on the gas or not. Very annoying if you were trying to inch down a trail in low range at 1100rpm and all the sudden the rpms kick up to 1800 on there own. I’ll check the tune number on my computer tomorrow, maybe the timing adjustment and stepper are something the auto computers adjust differently
 

efacewin

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Jun 11, 2017
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Not completely, the computer can still adjust the timing changing the rpms a few 100 in either direction. I tried unplugging the stepper motor when I was having erratic engine speed fluctuations when in low range on my last camping trip and it helped but the engine speed still varied at low speed without me changing my pedal position. Unplugging the VSS completely smoothed things out. I have no idea why but the computer was advancing the timing as soon as the vehicle started to move. Reguardless of if I had my foot on the gas or not. Very annoying if you were trying to inch down a trail in low range at 1100rpm and all the sudden the rpms kick up to 1800 on there own. I’ll check the tune number on my computer tomorrow, maybe the timing adjustment and stepper are something the auto computers adjust differently
I’m pretty sure it is true that the tune number deals with the those adjustments differently for the manual. It looks like tune # 9630, 9644 and 9653 are all the manual transmission tunes. I am currently trying to determine if the corresponding EPROMs can be copied and duplicated.