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Discussion Starter · #1 ·
Hey guys, I got a quick question.. I have a 93 5.0, I have a hanging idle, and it seems like my throttle cable sticks upon starting it up (when i push down on the gas pedal, it sticks, then it releases) I replaced the throttle cable, then i checked the TPS voltage and its at 4.12??? LOLLLLL i know where it should be (.98-.90), i believe this is my problem, with the idle.. So i replaced the TPS sensor, and it is still pulling 4+ volts.. I'm using the red and green wires to check voltage..

red - red
green - black

Any ideas where to look next? Already checked vacuum leaks, and corrected the problem..

All advice is greatly appreciated...

thanks guys
 

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put your meter positive(red) on the green and the negative(black) on the black for check tps voltage
 

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it really doesn't matter what lead you put on what....just put one lead on the green wire (I stuck a pin through the insulation to take my reading) and take the other lead and get a good ground with it...I just wedged it in a small hole on the side of the engine bay.
 

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Discussion Starter · #4 ·
Thanks guys, I'll recheck the voltage.. I am at a loss here.. I've had a hanging/surging idle before on previous mustangs, and it has always been a vaccum leak.. Has the gas pedal ever been locking up, then you have to actually step on it to open the throttle body? thats what it almost feels like? i'm going to pull the throttle body off, and egr, maybe it sucked up a piece of ***** somehow..haha.. It's really giving me a headache.. It also doesn't help being 20 degrees in my garage...

Any other ideas, or suggestions are welcome

thanks again
 

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Discussion Starter · #5 ·
I'm going to buy a new set of O2 sensors tomorrow.. Before this idle problem, It had a cold start problem, I did a tune up: cap/rotor, plugs, wires, fuel filter, and coil.. and changed the oil again.. This was the fix for the cold start problem, but the same day, the idle started to surge to 2000rpm, and stay there.. It still doesn't make sense why the gas pedal is so hard to engage upon starting it.. It may be the O2's.. I somehow looked over that, I think the problem lies in the t-body..

thanks again guys
 

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It does matter which wires because the black wire is what the computer reads as "ground" and it can be a different voltage than true ground.
 

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FYI.... What kind of throttle body do you have? Aside from double checking the voltage, if you have a BBK throttle body, as I used to have, the throttle plates stick. I remember feeling the gas pedal stick but by this I mean it kind of stuck closed and when you pressed on the gas, it felt like it stuck at the beginning.

Maybe something to check also.
 

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bigdaveg said:
I'm going to buy a new set of O2 sensors tomorrow.. Before this idle problem, It had a cold start problem, I did a tune up: cap/rotor, plugs, wires, fuel filter, and coil.. and changed the oil again.. This was the fix for the cold start problem, but the same day, the idle started to surge to 2000rpm, and stay there.. It still doesn't make sense why the gas pedal is so hard to engage upon starting it.. It may be the O2's.. I somehow looked over that, I think the problem lies in the t-body..

thanks again guys
I doubt it's the O2 sensors. cold start strategy does NOT use O2 feedback...Not until you at operating temperature.

I have the same car....had the same problem
I would look at all vacuum hoses. Especially, the hoses under the upper plenum. They suffer heat rot and are difficult to inspect because of their location.
Follow all vacuum hoses. Including the hoses to the charcoal canister.
Verify the PCV valve is seated in its gromet.
What is your TPS voltage when the car is idleing. Should be below 1 volt (and not 0.999999995 volts...I hate that !)
Have you had the upper or lower or egr spacer/throttle body off lately? If yes, is it possible you have un-metered air entering the system. This will cause erratic idle and force the O2 system to oscilate unnaturally- contributing to drivability issues.

I would clean the IAB valve very thoroughly. This is always an easy place to start. When the car is at operating tempeature and idleing, unplug the IAB electrical plug. What happens? Does the engine rpm drop, increase or do nothing?

This should keep you busy for a while.
Keep us posted.

That should keep you busy.
 

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Discussion Starter · #9 ·
yes i cleaned the IAB, I should of noted that.. As far as the vacuum leaks, I am going to double check the vacuum hoses again.. just to make sure.. I never had the upper off, but i'm assuming its a leak somewhere i didn't catch.. The throttle body is stock, and the car only has 110,000 on it.. I replaced the throttle cable, not as difficult as a clutch quadrant =) I will check the voltage again, Idwitheld_1 did you have the annoying problem with the throttle cable, and pedal? This is a first for me i'm on my 14th foxbody..

Oh well you learn something new everyday!!

Thank you for the replys guys, i'll let you know what happens tomorrow morning..

thanks again
 

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idwitheld_1 said:
I doubt it's the O2 sensors. cold start strategy does NOT use O2 feedback...Not until you at operating temperature.
But it uses the information it has gotten from prior closed-loop operation to adjust its idle fuel strategy even if it isn't taking input from O2's when cold. New O2 sensors can and will affect idle because of this.
 

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Sounds like you need to pull that throttle body off and clean it GOOD!

110,000 mile stocker? SURE to be gummed up.

check your throttle cable ROUTING. I had the same issh. moved the cable to follow a different route (only slightly) and its sweet now.
 

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broncobuddha said:
if you have a BBK throttle body, as I used to have, the throttle plates stick. I remember feeling the gas pedal stick but by this I mean it kind of stuck closed and when you pressed on the gas, it felt like it stuck at the beginning.

Maybe something to check also.

very true, same happens to mine. i cleaned the throttle plate when i first got my car though and helped a LOT. still does it minorly though. my bro has an accufab and its like pushing on nothing compared to mine
 

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i think your probing the wrong wire.
red - is usually your reference voltage which should be at or a little lower than 5 volts.
black will of course be your ground
the middle or different color wire is the one that needs probing which would be your signal wire or what your computer is reading

on my 89' its the DG/LG and BK/W wire that needs probing/
 

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Discussion Starter · #14 ·
God damn vacuum leaks!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Fixed finally!!!!!!!!!

I really appreciate the help bros, I pluged up like 6 holes at that vacuum tree by the thermoacters... now she idles right at 1000rpm!!!!!!!!!1

As far as the sticking pedal, I took the T-body off and took the butterfly out (little brass plate) cleaned it very well, dropped it back in, now it works like a charm!!!

I can't say thank you enough guys!!!!

Take care

Dave
 

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MFE said:
But it uses the information it has gotten from prior closed-loop operation to adjust its idle fuel strategy even if it isn't taking input from O2's when cold. New O2 sensors can and will affect idle because of this.
Just a thought...what does it do on the first time? Where does it get A/F strategy info? I assume it has a "default" table? Also, does this clear after taking the battery off for a period? I have read about this fuel economy strategy or "adaptive learn mode" before and was wondering if it was the same thing? I was under the impression this was for fuel economy strategies only.....

Just currious how that works. I am so fascinated by the EEC...and it's secrets.

So glad the problem was fixed. It usually ends up being something basic like vacuum. Great board. Great help.
 

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Yes, it has tables it relies on at first and also to replace missing information with if a sensor fails. Then it uses what it sees from the O2 sensors under varying conditions in what is called Adaptive memory to both optimize economy and, more importantly, keep the car running properly as systems age and things go "out of tune". One thing a lot of people don't realize is when they screw with fuel pressure on the dyno to affect a/f ratios and power, the computer compensates the changes back out by the time the car is driven home.

There is a ton of good EEC info out there...here's a good start, THe guy who wrote these articles is an EEC guru: http://www.mustangworks.com/articles/electronics/

There's also a great book by Charles Probst that explains a lot of this stuff in relatively layman's terms. Every 5.0 wrencher should own it.
 

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The ford electronic fuel injection....by Probst is very informative. Probably the best "tool" I have purchased for my mustang yet.

Thanks for the link too!
 
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