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Poorly running 89 2.9


Mightyfordranger

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That line your talking about that's looped. Its a hard plastic line with rubber ends. I think that's my map sensor. I seen other videos where the first gen 2.9s had the map as a little sensor bolted to a stamped sheet metal bracket. I don't have that it goes straight into the firewall.
The one I have tide to the intake just goes to the air box. No idea what it does but the factory one was broke so I just ran that one.
I took it out for a spin it does run better overall and I couldn't get it to do that awful stumble it had before. So it will come on power normally now.

I must have done something to help vaccum overall because now my brakes aren't near a squishy as they were before, the thing thing can actually stop now.

But the thing is it still carries a high idle inbetween gears its weird it seem like it will gain like 300 rpm when your just Rollin up to a stop sign, once stopped it will take a sec then drop back to idle.
This is under no throttle input
 


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Mightyfordranger

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I'll make another video real quick
 

Mightyfordranger

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franklin2

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Your throttle is set way to far open. When you unplugged the IAC the idle speed should have dropped way down, it may even almost stall. Having it this far open is probably also messing up your throttle position sensor voltage. This assumes you do not have a large vacuum leak, which I think you have been over it pretty well to eliminate that. But you will find out in a moment;

Get it running again like you had in the video. Unplug the IAC like you did in the video. Then go over to the throttle stop screw and back that out till the engine barely runs. Then plug your IAC back in. Let it try to sort itself out. Then turn it off for a minute, restart it, and see what you have. You can rev it a little bit, and stop and restart it again, or just drive it for a little bit till it get's itself sorted out.

Your IAC can't work, but there is too much air going by the throttle. The IAC is pretty much shutting itself off most of the time, because it can't bring the idle down where it wants it.
 

Paulos

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Here's some interesting information regarding newer IAC's in pre-'89 Rangers.

And Ford's procedure ('87 manual) to adjust the idle if the throttle plate screw has been turned.

20200410_171224 trimmed.jpg
 

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franklin2

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Interesting about the newer IAC valves. I am hoping his is working, he does get a little rpm increase when it's plugged in. And I think you will agree, when he unplugs the IAC, he is way above 650 rpm. I would not worry so much about being exactly at 650 rpm with it unplugged, but it does need to be at a very slow idle with it unplugged.

You have a certain amount of required idle air, a certain small percentage should come from the throttle blade, the rest of the idle air comes from the IAC. This gives plenty of latitude to the computer to control the idle speed.
 

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I think most people see that screw as a simple idle adjustment (I probably did years ago also). From what Ford shows, it's a calibrated adjustment. I did the adjustment on mine a year or so ago. It took a little while for my ECM to finally adjust the idle to normal afterwards. The idle didn't like to come all the way down very quick when shifting gears, but it eventually did.
 

Mightyfordranger

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That's a weird system. Almost have to re teach it. But alright I did monkey with that screw a tad today. I backed it off like 1/2 turn. Maybe it needs more? Idk I never messed with it before that. So as far as I knew that screw hadn't be turned in 30 years till. I gave it a squeak today.

But I'll do the little procedure posted above and uh see what the deal is.

As for the TPS I explained how I installed it did I rotate it the wrong way? If I did you'd figure it would have broken right?
 

franklin2

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Turn that screw way back, slow that thing down. They designed the computer to have control of the engine in every way possible. That includes idle speed. I would not be surprised if you pulled the codes and you already have a code 16. The computer will set a code 16 if the engine speed is too high and it can't bring it down. Code 17 will be set if the speed is too slow and the computer can't bring it up.
 

franklin2

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I think most people see that screw as a simple idle adjustment (I probably did years ago also). From what Ford shows, it's a calibrated adjustment. I did the adjustment on mine a year or so ago. It took a little while for my ECM to finally adjust the idle to normal afterwards. The idle didn't like to come all the way down very quick when shifting gears, but it eventually did.
This has been my experience also. After I set it, I was a little disappointed in how it idled. So I kept driving it while contemplating what I was going to do next, and a couple of days later driving to work it straightened itself out. But that was after I had set the idle speed way down with the IAC unplugged. If I were to guess, I was probably more like 500 rpm with the IAC unplugged.
 


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