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Discussion Starter #1
Stock foxbody efi setup. Sometimes while running perfectly, rpm will hang at around 2k and not go lower than that until I turn off key. Restart returns everything to normal. I have a bit of blowby and wondering if a oiled up 02 sensor could be the cause. I’ve done the usual base idle setup, checked tps, iac etc.
 

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O2 sensor has nothing to do with it.
 

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Dean Scheidt
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I had a similar condition on several occasions with my 1989 GT. Mine was always related to the 10-pin connectors (aka salt and pepper shakers). Next time the idle is hanging, try moving the 10-pin connectors around to see if the engine idle changes. If so, look up 10-pin connector fix.

Dean
 

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Stock foxbody efi setup. Sometimes while running perfectly, rpm will hang at around 2k and not go lower than that until I turn off key. Restart returns everything to normal. I have a bit of blowby and wondering if a oiled up 02 sensor could be the cause. I’ve done the usual base idle setup, checked tps, iac etc.
the next time it hangs

do NOT shut off the engine, put in park or neutral, e-brake on

pop the hood, get out, walk to the front of the car, open the hood, prop the hood

then

disconnect the IAC connector..........what happens?
 

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Discussion Starter #7
Thanks for the suggestions. I’m on my 3rd iac and tps, and serviced my 10 pins last year. Servicing the 10 pins did solve some other issues I was having. About the TB butterfly....do you mean like a physical hanging of the valve? I wouldn’t think that would be the issue as a restart clears the problem. Gotta be sensor/electrical/eec related.
Next time it does it I will pull over and start jiggling stuff. Will jiggle stuff on the engine too ;j
 

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Discussion Starter #8
the next time it hangs

do NOT shut off the engine, put in park or neutral, e-brake on

pop the hood, get out, walk to the front of the car, open the hood, prop the hood

then

disconnect the IAC connector..........what happens?
Will do.
What is the diagnoses for each scenario? I’m guessing there are 2 outcomes......it’s either makes no change or idle drops back down.
 

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engine requires air to run

in order for the engine to run at 2000rpm, air must be entering

and dont be jumping to conlusions, that it has to be a sensor or elec issue

start at the source then gain direction....
 

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Discussion Starter #10
engine requires air to run

in order for the engine to run at 2000rpm, air must be entering

and dont be jumping to conlusions, that it has to be a sensor or elec issue

start at the source then gain direction....
Happened again. Jiggled the 10 pins, no change. Unplugged IAC and idle dropped to normal. Plugged back in idle jumped again. This is a nearly new Motorcraft IAC on it.
 

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Discussion Starter #11
Happened again. Jiggled the 10 pins, no change. Unplugged IAC and idle dropped to normal. Plugged back in idle jumped again. This is a nearly new Motorcraft IAC on it.
So a little further sleuthing. I noticed that when idleing normally when i pulled the IAC connector, there was no change in idle where you would expect a drop. I redid the base idle procedure and all seems good for now. I did have to back off the idle quite a bit, checked TPS and I’m back in the .9xV range. I should have checked the TPS voltage before adjusting, but I think I had the throttle adjusted out of range of the TPS.
 

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Happened again. Jiggled the 10 pins, no change. Unplugged IAC and idle dropped to normal. Plugged back in idle jumped again. This is a nearly new Motorcraft IAC on it.

so.............

read what you wrote regarding the IAC, forget the 10 pin stuff for now

after reading what you wrote for the IAC, why would you think it is faulty?

HINT: this is a duty cycled solenoid, requires power, on-off quickly

you remove power, what will happen?
 

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So a little further sleuthing. I noticed that when idleing normally when i pulled the IAC connector, there was no change in idle where you would expect a drop. I redid the base idle procedure and all seems good for now. I did have to back off the idle quite a bit, checked TPS and I’m back in the .9xV range. I should have checked the TPS voltage before adjusting, but I think I had the throttle adjusted out of range of the TPS.
this is a stock engine, you are doing a idle reset on?

normal TPS range is 0.65-1.15Volts, if it falls within this, leave it alone
 

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Discussion Starter #14
so.............

read what you wrote regarding the IAC, forget the 10 pin stuff for now

after reading what you wrote for the IAC, why would you think it is faulty?

HINT: this is a duty cycled solenoid, requires power, on-off quickly

you remove power, what will happen?
Thanks man. I appreciate you’re trying to help me learn this on my own rather than spoon feeding me the answers. That’s exactly what I need.
To answer your question......I don’t think the IAC is faulty. It was reacting to the input it was receiving from the eec based on info it was getting from the TPS. Am I on track here? Power removed from IAC makes it close would be my assumption.

this is a stock engine, you are doing a idle reset on?

normal TPS range is 0.65-1.15Volts, if it falls within this, leave it alone
Correct, stock engine that was refreshed with rings and gaskets. As i mentioned, it is pretty loose. Plan is to pull it over the winter and have the local engine shop go over the block and assemble my shortblock.
Anyways went out for a few hrs tonight and no idle hang issues. Still have my low speed bucking issue, but no idle hang.
Thanks again for the coaching.
Brad
 

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you may not have the throttle blade in the perfect, "expected" value, it may learn over time or not

the bucking is usually a good indication the blade is not in the correct position

as the IAC, is opening and closing during cruise when it shouldn't

time will tell
 

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look up the the throttle body air flow scalar in your ecm

then set it to that number while looking at real time air flow data stream from the maf

or measure you throttle body air from maf data, and input into the ecm

both will require use of tuner with data logging in real time


that is why ford clearly stated to never adjust the stop, as idle is set in the ecm
 

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My numerous experiences with erratic/ hanging idle and low speed bucking over the years has lead me to find these conditions as possible sources-

•Voltage too low. RPM increases to speed up alternator.

•Idle RPM too low.

•Vacuum leak.

•Dirty or mismatched MAF.

•Fuel trim incorrect

•Clogged fuel filter/fuel pump issues.

• Bad ground.
 

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My numerous experiences with erratic/ hanging idle and low speed bucking over the years has lead me to find these conditions as possible sources-

•Voltage too low. RPM increases to speed up alternator.

•Idle RPM too low.

•Vacuum leak.

•Dirty or mismatched MAF.

•Fuel trim incorrect

•Clogged fuel filter/fuel pump issues.

• Bad ground.
To add to this, I have seen a corroded positive battery cable cause this as well. It always seemed to happen after an instant heavy load was put on the battery such as the fan turning on.
 

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Discussion Starter #20
Thanks for the replies. Thought I had it licked, but it happened again tonight. Regarding voltage....might be onto something there. Ever since I did this conversion I have had flickering headlights when at idle. I’ve tried raising idle, but that causes TPS issues. I’m running a 3G alt and have no charging problems and battery voltage is normal. What would be a good way to eliminate this as a cause?
With the help from this great resource of talent and experience, I’ll get this sorted. Thanks guys.


edit: I should mention the battery is in the trunk and I’m using the stock 2awg wire from the trunk to the engine bay.
 
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