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Discussion Starter #1
I just barely bought my bronco today it is a 1993 with a 5.8 351 and it was obvious that there was something wrong with the idle. Here is what happens
I turn the beast on and it rises to about 2000-2500 RPMs
and so i thought that maybe if i let it sit it will stop but it didnt so i tried to give it a little bit of gas and it still didnt drop down
and the other thing is my idle speed is around 25 MPH
what worries me is that i will destroy my transmission because every time i put it in gear it jumps forward even with my foot on the brake
if anyone can help that would be great
Thanks
 

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Sounds like the IAC is sticking, but if it had this problem when you bought it I wouldn't doubt if some jerk tried messing with the idle speed stop screw to try and fix it. Either way, test the IAC first and DON'T TOUCH THE SCREW, unless it was moved before, then your in for some fun.
 

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Discussion Starter #3
K so i took off the IAC and cleaned it a little bit with Q-tips and that brought the idle down to about 1700 but then it went back up to 2100 and that is where it currently idles at
so i am going to replace the IAC and then go from there
 

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Ha, bet tis the TPS, I ran into the very same issue with my 5.0 Lincoln last year. Could be the ECT or ACT sensors as well, but in my case it was the TPS. Got a spare one floating around? Or a junkyard where you can snag one for free?
 

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Make sure its not the throttle cable by disconnecting it. Sometimes they rust up or the plastic housing breaks causing it to stick. Pull codes too. It could be a vacuum leak also.
 

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Discussion Starter #6
ok well i will have to find out what it is
cause i replaced the idle control valve and then it brought it down to 1700
There is a a hose on the left side of the engine that comes up from the block that blows hot air out and i don't know what that is
and near that hose is a little canister with a connection for a 1/2'' hose on both sides
If anyone can tell me what that is and if it will fix my problem
that would be great
thanks
 

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rule of thumb - anything that blows is not a vacuum leak - vacuum leaks suck, literally. I think what you're looking at is the warm air supply for the intake ducting, supposedly it helps the engine idle better on cold starts and also warm up faster. As far as the canister goes, I'm thinking tis some sort of a vacuum reservoir, but I ain't sure on that.
 

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Discussion Starter #8
ok well then i dont think thats my problem
and the throttle does not stick,
i dont know how to check and see if the TPS is working
so if someone can tell me how to do that (if it is possible) that would be great.
 

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Pull the codes and post up.....and no, the CEL does not have to be on for their to be a code.
 

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Satyr of the Midwest
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the throttle does not stick,
Did ya actually disconnect the throttle cable from the throttle lever to see whether there's a difference in how it feels at off-idle and returning to the closed position? Just because you don't feel it sticking with your foot doesn't mean it's not hanging open a little; even a few degrees of opening it will cause a large difference in idle speed.

i dont know how to check and see if the TPS is working
so if someone can tell me how to do that (if it is possible) that would be great.
 

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I think what you're looking at is the warm air supply for the intake ducting, supposedly it helps the engine idle better on cold starts and also warm up faster.
I think what he's talking about is the thermactor bypass outlet.
 

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with it idleing push the bracket up against the stop screw to make sure it is returning to position. See if that changes your idle.

search for the tps thead, it shows how to check the tps. Check it and make sure it is fine.

If that don't work, pull codes.
 

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Discussion Starter #13
ok well i have been too caught up in the idle issue that i just barely replaced the spark plugs.
And 7 of the plugs were the 93 original plugs that were worn completely out.
I did disconnect the throttle cable and it didnt change the idle and i sprayed engine starter fluid around some places and the idle didnt increase so i havent found a vacuum leak.
Now if it was the throttle position sensor, shouldnt the check engine light be on
cause mine isnt on.
I will try to pull codes tomorrow after school in auto mechanics. so i will let everyone know how that went

thanks for all your input
 

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Satyr of the Midwest
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No, the PCM will usually NOT throw a code for for a TPS problem. You've got to backprobe the TPS line for its voltage.
 

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Discussion Starter #15
i dont really know how to backprobe the TPS
and i havent been able to locate it either.
Maybe someone can throw a link to somewhere that shows how to do it.

thanks guys
 

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Mine did the same thing with the bad TPS too. Idled really high. Jumped into gear because it was high RPMS. Is it bucking from 1st gear to 2nd? If so, I didn't notice where you mentioned that. It would indicate the truck is in Limp Mode.

You can't find the TPS? It's going to require a little effort. You can search here and you'll find it no problems. I have a 93 with a 351, so you'll probably need to pick up a throttle body gasket as yours is probably toast (hint - you'll be removing your throttle body to do this unless you're one of the fantasic 4 and got rubber arms) lol
 

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Satyr of the Midwest
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The TPS thread covers how to backprobe the TPS.
 
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