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Foc'd off

Sorry To Ask, Another Idle Problem!!

26 posts in this topic

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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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

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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!

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youre iac is knackered its really that simple

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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!

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

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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

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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

deanoo likes this

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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.

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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

soulman123 likes this

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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

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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

soulman123 likes this

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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!

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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

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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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Let's not get into an argument over this. All I really want to know is why my IACV is holding open at any temp or rev setting.

My bets is a damaged ECU/PCM module but I would still appreciate any feedback on this!

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Simply put from experience try another icv at 80k its well past the usual change interval its cheaper and simpler than messing with ecu pcm if the icv does not cure the issue then its common to have a faulty throttle body the ecu pcm being expensive to repair would be my last port of call if the icv is faulty it will stick open normally we just swap it with a working one to check takes 5 mins to do i am being genuinely honest not trying to argue all idle issues ive had either the same or similar to youres was resolved with a new icv including my own old mk1

Pcm faults with youre issue are so rare without other symptoms

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no arguments here...all about info and opinions

think what your missing arts, is IAC is being held wide open, have never come across this myself but in order for it to do that it has to be supplied a constant 5v...[maybe 12, cant remember] which indicates a wiring short or more likely a pcm problem...

pcm/ecu's are common problems to those in the trade...have sent two away for repair already this year.

its possible the short is within the IAC, which should easily be eliminated with a resistence test...

in all the years, i have only ever changed a handful of IAC'S over a multitude of makes, often the problem is just cleaning, some its cheaper to change, others its cheaper to clean...

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Im not in the trade anymore but have changed a fair amont of icv valves collapsed hoses and pcv valves why its so common on tge focus compared to others i have no idea ive never come across the pcm causing the issue im not saying it isnt the case but if i was hinging my bets it would be the icv or the wiring plug to the icv which can suffer from corrosion or get brittle from the heat ive always found on the fords with these types of issues they are never as simple as other makes sadly the ford icv never responds to cleaning myself and many others who had the mk1 all had to replace it at around 50-60k due to similar issues

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would agree with a lot of that, just the fact its fully open on connection, closed at disconnection, so not sticking, that indicates to me a signal problem, add to the mix info about pcm accident damage, increasingly looks like the brain or associated wiring/connections....but could equally be something else is fooling the ecu into believing engine needs more air to idle...

my money is on pcm related....but diagnosing over net is nigh on impossible

but hey...if it was easy, id be scratching for work :)

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Its an unusual one i dont deny it ide still be tempted to pop a scrap one in to see what happens

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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

I'll go out and check these now and report back, I'll also be taking a more thorough look at the condition of the wiring for frayed/earthing wires corrosion etc.

Thanks all for your comments!

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Well I'm no nearer to a solution than before.

First I measured the IACV, that comes back as 9.7 ohms, the plug on the loom shows one pin at 12.8v and the other appears to be earth. I was wondering why bother to have an earth wire to the IACV when it could easily be done through the chassis ground?

Anyway, I removed the ECU and stripped it to find masses of metal filings inside, some were on the legs of a rather large processor looking chip. I removed all the dust etc and rebuilt it. Still no difference, the IACV holds fully open no matter what.

Whilst I'm thinking about this, does anyone know the travel of the IACV piston? Mine only moves about 3mm from shut to fully open!

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from memory and it was a while ago it was around 4mm

you may need to replace or have the ecu rebuilt i know bba reman state the diodes have a habit of failing but again this will cost money this may be one of those issues that just goes on and on

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First I measured the IACV, that comes back as 9.7 ohms, the plug on the loom shows one pin at 12.8v and the other appears to be earth. I was wondering why bother to have an earth wire to the IACV when it could easily be done through the chassis ground?

should have green/yellow wire [supply] and black/yellow wire [signal]

it could be with engine off, this signal wire is earthed through the pcm, be interesting to know if you still get earth with engine running, if so, then think your almost definitly getting a short in pcm/wiring.

as said before, that wire should be averaging a 3 volt switching signal, maybe worth checking if your getting an earth with IAC both connected/disconnected whilst running.

not forgetting that signal would be too fast for voltmeter to handle, but if its earthed then should show up

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