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 Post subject: isc circuit problem
Posted: Thu Oct 05, 2006 11:23 am 
Oompa Loompa
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the ef idles low when start up cold but when warmed up its ok. i back probed the isc at its harness, not at the ecu, with the ignition on i get just under 12v but the voltage goes up when engine is running, 13-14v, and when i applied load to the engine with air con. or headlights, the voltage is supposed to drop but it stays the same, any suggestions, thanks.
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Posted: Thu Oct 05, 2006 12:17 pm 
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replace it.

 

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Posted: Thu Oct 05, 2006 1:27 pm 
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How would replacing the unit help if the controller isn't controlling right according to his post?

ef_ford - Just to confirm, rip the ISC off, and close up the holes on the throttle body, and start it and hold the throttle open and just turn AC on, and put load on it, and have a look at the ISC, see if you can see it open.. even while cranking.


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Posted: Thu Oct 05, 2006 5:00 pm 
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because if it's not working a replacement will indicate if it's isc or not,,normally once they start playing up they are stuffed.

 

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Posted: Thu Oct 05, 2006 7:03 pm 
Oompa Loompa
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got a spare i can use lol, dont think changing it will solve the problem if voltage isnt right, i checked the resistance on it and it is normal, thought maybe the valve was sticking so i soaked it in terps, still seems sticky lol. the manual says that voltage should be between 8-12v depending on engine load so i dont know why im getting 13-14v.
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Posted: Thu Oct 05, 2006 7:19 pm 
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well it's either the isc or the ecu,,take your pick.

 

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Posted: Thu Oct 05, 2006 8:02 pm 
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As naughtyfalcon said, or any of the sensors leading to the ECUs decision, or grounding. It can be lots of things.

Run a diagnostic check on your ECU, see what you come up with,

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Posted: Thu Oct 05, 2006 9:55 pm 
Oompa Loompa
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checked ecu diagnostics, the only thing that came up was in engine running mode 411/412, which is low/high idle speed failure.
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Posted: Thu Oct 05, 2006 10:09 pm 
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well it sounds like your isc is stuffed.

 

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Posted: Thu Oct 05, 2006 10:54 pm 
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naughtyfalcon wrote:
well it sounds like your isc is stuffed.

Seriously you're giving him 2 options, ISC or ECU... Unfortunately it goes deeper!

He PM'd me today as he seen a thread that i posted in about this issue, my EF had this problem and i never found out what the problem was, i changed every single sensor, tried an ECU, changed engine harness, still didn't fix it.
I put it on my mates diagnostic machine and it came up with power steering switch, that wasn't it either.... In the end i turned the base idle up and just drove it as i couldn't be stuffed finding it.
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Posted: Thu Oct 05, 2006 11:53 pm 
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power steering switch lol typical ford aye,,well that was all i can think of,,it's either the isc or the ecu,,don't forget no two cars are the same...

 

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Posted: Fri Oct 06, 2006 12:06 am 
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That's right, no 2 cars are but the problem is the same, and i've known of many others with the exact same problem.
And you are so sure it's ISC or ECU, hmmmm i tried both and never solved my problem... I also changed air temp sensor, coolant temp sensor, engine harness, power steering switch, even the BEM i got that desperate.

I hope it turns out to be a simple fix ef_ford, i actually have to look at my mates EF, it has the same problem.
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Posted: Fri Oct 06, 2006 12:35 am 
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s**t walker, you've really tried it all lol. The next thing Id be trying is testing all the pins. Your gregories manual (or ford workshop manual if you have one) will show what is required from each pin. The ECU obviously has a reason for doing what it's doing. And I wouldn't say its the ECU because its still doing its job (controlling the ISC), just not right. So the hardware is obviously functioning in the ECU.

Did it just start doing it out of nowhere?


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Posted: Fri Oct 06, 2006 12:47 am 
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LOL yeah, i started to test each wire for voltage, continuity etc, but i got the s**t and walked away, i should have kept at it lol.
The car is gone now so it doesn't matter.
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 Post subject: Re: isc circuit problem
Posted: Fri Oct 06, 2006 2:19 am 
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ef_ford wrote:
the ef idles low when start up cold but when warmed up its ok. i back probed the isc at its harness, not at the ecu, with the ignition on i get just under 12v but the voltage goes up when engine is running, 13-14v, and when i applied load to the engine with air con. or headlights, the voltage is supposed to drop but it stays the same, any suggestions, thanks.


could always go back to basics and clean all the carbon out of the throttle body, after a while it builds up around the butterfly and restricts airflow - the isc will only let 'so much' more air in, which probably isnt enough, when the car is cold.

To test the isc, disconnect it with the car running, if it nearly or does stall, the isc is working. While its disconnected, set the base idle, around 600 rpm, will be fine.

The isc will always have battery voltage to it when the key is on, and will most likely have battery voltage showing on both wires, because the ecu provides a ground to the isc, but it is a pwm signal, therefore most multimeters will have a hard time reading it correctly. If you have a multimeter with a frequency range (Hz), try that, you should be able to see a varying frequency on the ecu side of the isc.

Also you should check the TPS voltage and Map sensor frequency, i've had falcons hold revs when hot which was caused by faulty map sensor.
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