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Sorry To Ask, Another Idle Problem!!


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#1 Foc'd off

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Posted 06 April 2013 - 02:50 PM

My apologies for registering and diving straight in with a problem but I'm at a loss!!

 

The story as follows.

 

My Focus is a 2002 1.4 with only 80,000 miles on the clock. The issue with it is the idle air control valve opens fully causing the engine to idle at ~3000 rpm's.

With the IACV disconnected the engine will stumble when cold but idles perfectly when warmed up.

 

I have checked about everything I can find, and did find the PCV hose was collapsing so I replaced that at a cost of £17 from Fords. I then did a ECU reset and reconnected the IACV but this made no difference with the engine still idling at over 3k.

 

Now comes the hard to answer question.

 

How would an IACV typically fail and would one fail in the open position?

 

When the ignition is on and whatever the state of the engine (running or not), if I connect the loom to the IACV it will pull fully open.

 

If not the IACV being faulty, I'm suspecting the PCM is the culprit.

 

Thanks in advance for your help!



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#2 FOCA

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Posted 06 April 2013 - 05:39 PM

You could bodge a remote for the IACV and switch it on for starting and off when warmed up, it would bo easy and cheap to do, you could hide the switch under the dash etc  



#3 Foc'd off

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Posted 06 April 2013 - 05:44 PM

You could bodge a remote for the IACV and switch it on for starting and off when warmed up, it would bo easy and cheap to do, you could hide the switch under the dash etc  

Thanks for your answer but I'm really not looking to do a bodge, I just want to find out what is causing this problem so I can do a proper fix!



#4 artscot79

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Posted 06 April 2013 - 06:05 PM

youre iac is knackered its really that simple



#5 Foc'd off

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Posted 06 April 2013 - 06:24 PM

youre iac is knackered its really that simple

Can you give me something more to go on? Saying it's knackered is one thing but do you know of one where it opens fully?

 

In otherwords, is the PCM putting out a higher voltage to cause it to open or is there another reason? My engine has a TPS tested ok, TMAP sensor tested ok, PCV hose found to be collapsing and replaced, ECU reset made no difference.The IACV voltage is at a constant high, I suspect it's the PCM module, saying it's the IAC is a poor answer considering the above!



#6 deanoo

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Posted 06 April 2013 - 06:43 PM

I have no idea what you guys are talking about so many acronyms I'm going to declare myself out lol.



#7 wase16ll

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Posted 06 April 2013 - 06:49 PM

iac isnt the easiest to test without an oscilloscope..
you can do a basic resistence/supply test of iac

disconnect wiring, test at iac

should have approx 9.5 ohms between terminals 1 and 2

disconnect wiring, ignition on, test at harness plug

11-14 volts between terminal 1 and earth

beyond that you need to test at pcm iac signal with oscilloscope...should have a switching voltage of approx 3v, with hot engine at idle, the speed of that switching would be way to fast for a voltmeter to cope with

im inclined to agree with you in that chances are its pcm/wiring, unfortunately been a long time since ive tested one, autodata doesnt give anymore than above info.....best bet, if resistence/supply is ok, get a scanner that can read live data, chances are that will show what the pcm is doing

#8 Foc'd off

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Posted 06 April 2013 - 06:53 PM

I have no idea what you guys are talking about so many acronyms I'm going to declare myself out lol.

Let me enlighten you.

 

PCM = Power Control Module

TPS = Throttle Position Sensor

TMAP = Thermal Manifold Absolute Pressure Sensor

PCV = Positive Crankcase Ventilation

ECU = Electronic Control Unit

IACV = Idle Air Control Valve



#9 Foc'd off

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Posted 06 April 2013 - 07:01 PM

iac isnt the easiest to test without an oscilloscope..
you can do a basic resistence/supply test of iac

disconnect wiring, test at iac

should have approx 9.5 ohms between terminals 1 and 2

disconnect wiring, ignition on, test at harness plug

11-14 volts between terminal 1 and earth

beyond that you need to test at pcm iac signal with oscilloscope...should have a switching voltage of approx 3v, with hot engine at idle, the speed of that switching would be way to fast for a voltmeter to cope with

im inclined to agree with you in that chances are its pcm/wiring, unfortunately been a long time since ive tested one, autodata doesnt give anymore than above info.....best bet, if resistence/supply is ok, get a scanner that can read live data, chances are that will show what the pcm is doing

Thank you for your reply, i may also suspect it's the PCM since I found it was damaged due to a previous accident. I will drag the ECU/PCM out and see what's going on. I have access to a scope but in all honesty I can't be asked when the only problem is a low idle when cold!! With the IACV disconnected it's fine when warmed up.



#10 deanoo

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Posted 06 April 2013 - 07:11 PM

Let me enlighten you.

 

PCM = Power Control Module

TPS = Throttle Position Sensor

TMAP = Thermal Manifold Absolute Pressure Sensor

PCV = Positive Crankcase Ventilation

ECU = Electronic Control Unit

IACV = Idle Air Control Valve

Btw Thanks for taking the time lol 



#11 wase16ll

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Posted 06 April 2013 - 07:12 PM

been a long time since i tested one, cant remember if 5v for fully open or zero...but to me it sounds like you have a short or a break somewhere, if ecu was accident damaged then chances are the problem will be within the pcm or any wiring close to where the damage occured

#12 artscot79

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Posted 06 April 2013 - 07:27 PM

Its not a poor answer if its suspect it has to be replaced all the testing in the world wont change the fact that to eliminate it it has to be replaced

The idle control should balance the idle the easiest way to yell if its faulty is on cold start the car will go to 2k revs or more if disconnected with the engine running the engine doesnt die the iac is faulty trust me i spent a long time fixing these issues on my mk1 with the help of others on here to cause youre issue the iac is what you replace first it tskes specialists to properly test the system its way cheaper to replace the part so any garage will replace it the pcm at fault is not so likely diode faults are common in the pcm however these cause misfires more than anything the only othet possibility is a faulty throttle body causing excess air to get in the iac is about £20 the osciloscope diagnostics around £150 throttle body a good few hundred

#13 FOCA

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Posted 06 April 2013 - 07:56 PM

Thanks for your answer but I'm really not looking to do a bodge, I just want to find out what is causing this problem so I can do a proper fix!

 

Just do exactly the same thing but call it a modification instead of  a bodge :)  - it would be just be like having a manual choke

 

The switch would cost £2, how much will it cost to fix it "proper"

 

My mate's Focus had (probably, in retrospect) the same problem for years, it was a pain, the amount of times he was under that bonnet messing about disconnecting/ connecting it - he worked for Ford too!  



#14 wase16ll

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Posted 06 April 2013 - 07:59 PM

artscot
dont agree with that at all, he has already stated he carried out tests on various other sensors and ok'd them, so obviously has the equipment and know how to test the iac too once he knew what to expect..

from my experience with the job, i have often found wiring and connections are far more likely to be at fault than sensors, would go as far as 70/30 split...what people often assume is, when renewing sensors cures the problem, it was the sensor at fault, but its just as likely renewing sensor has just improved the poor connection...
in my game, i test everything, replacing is a last resort

#15 artscot79

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Posted 06 April 2013 - 08:40 PM

I do agree ive sorted 30 minimum its always the same change the icv if it doesnt fix it then you look at tge throttle body taking in too much air some parts have to be replaced this is one they are a common fail part the fact the car isnt attempting to stall with the plug disconnected points that way sometimes being over technical doesnt work ive never had a pcm wiring fault always tye icv wad the cause the icv can fail either open high revs when cold or closed where it stalls when warm or tge idle bounces it shoukd only idle at 700 plus or minus 30 when warm 670-730 is the correct idle speed if it fails closed then when warm if you rev the car the idle would drop to 500-600 rpm there is also a pcm update for that

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