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Discussion Starter #1
My 86 s-10 with its newly installed 87 2.8 idles at what I'm guessing 3000 rpm most of the time. The new motor came from a wreck. I got to run the motor and did not experience this. The ENTIRE motor was swapped.

Sometimes it will start at proper RPM, wait 30 seconds and then up it goes, real fast.

I tried installing the old temperature sensor by the thermostat in case it needed to be synced with the 86 computer. no change.

I'm quite sure I have all vaccum lines properly routed.

Is this an 86 computer to 87 motor incompatibility?

There has been one or two times so far that I could drive for half an hour at low RPM and I think things have settled down, then I come to a stop light and up go the revs for no reason at all.

I need some true direction on this one so I don't run around replacing expensive sensors for no reason. PLease help.Thanks.
 

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If the idle EVER goes up/down, you at least know that the ECM is hooked into the right spot, and has the ability to control the IAC motor.

Chance are that the IAC motor is just sticky, so you're getting the random action.

It's located on the drivers side of the throttle body, right below the TPS. Big square 4 pin connector.
 

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Discussion Starter #3
I see, that makes alot of sense. Does this mean I change it? If so, how? Messin with anything TBI is beyond me. I'm a 4 barrel kinda guy.
 

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It's no worse than changing a spark plug - ok, a BIG spark plug. :)

Just gently pull back the clip and remove the plug.
Then use a (24mm????) wrench or a 12" adjustable and unscrew it.
Check the new one's extended length (of the pintle) and make sure it's not poking out more than the old one. Screw it back in, and give a snug down (don't kill it). Hook back up, go for a drive. it should straighten itself out in the first 10 min's or so depending on the temperature.
 

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Discussion Starter #5
Nice play by play, greatly apreciated. By the way, for whatever reason, the high rev, low rev has stopped....i think, tommorows 1 hour drive to work will confirm this.

Question: I power washed the motor when I got it. I bagged the fuel ports really well but not the connection for the IAC.

This motor did not rev high when I got it from the wrecker.

Could this have been the problem? Wet connections?
 

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Good chance! It's just a little itty bitty stepper motor, and the water could have confused it. There's no feedback to the ECM from it, but still.... water and electrons rarely play well together.
 

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Discussion Starter #7
Thanks for helpin a fellow BC Bum. Y

ou backin' the Olympics? I'm in.

Thanks again
 

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Discussion Starter #8
Moving to a new thread

I have another problem to still solve and I think should start as another thread,hope you can help me there as well.

quinn
 

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You can bench test the iac motor to see how it's working.Remove it from the engine,and hook up a 9v battery to the first and fourth pins.It should either extend or retract.Reverse the polarity and it should do the opposite.That will tell you if it's responding to the computer's commands.
 
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