[Micky]

Mk3 1.8 petrol

Still trying to clear the intermittent poor cold start and hesitation. TMAP and engine coolant sensor changed, plugs 6000 miles old. IACV and throttle valve cleaned. Cold starting has been good over the last couple of days, but it was a pig this morning (temperature a bit lower). The IACV works with a "thunk" if I wire it straight to the battery, there appeared to be an intermittent 12v supply at the connection to the IACV and the wiring to the connector plug looked dubious. Me, my trusty side cutters and my soldering iron improved the connection to achieve a consistent 12v, I won't know till tomorrow morning if the problem has been cleared, but the IACV still doesn't "thunk" when energised, suggesting a high resistance connection further back in the wiring.

However, this doesn't fully match the symptoms, the hot idle is always good, cold idle also good when it starts. So, if all the IACV does is control idle then it's working OK. But if it also controls cold start and transistion over low rpm then there it might be the cause of the problem. Is there anything else that alters the amount of air admitted to the engine during cold starts?

I've rechecked the fault codes, now shows none (thanks Paul Young).

At this rate, I'll be paying someone to look at the thing

 

[DC]

the TPS (throttle position sensor) fitted to the side of the throttle body detects the how far the butterfly is open and the ecu adjusts the amount of fuel delivered dont know if thats of any use to you.

 

[Micky]

Thanks DC :L so it's possible that the TPS is sending the wrong information to the ECU when the throttle valve is closed, which would not be a good thing. However, the hot start is good.

The car has been sitting outside for a couple of hours, the IACV "thunks" now when the ignition is switched on, so fingers crossed. If it's a problem tomorrow morning I'll check the TPS.

With no voltage, the IACV is closed. With voltage applied it passes air. So the "thunk" is the sound of the valve opening. But is more air required at a cold start to raise the revs? Obviously, the ECU can control the richness of the mixture by increasing the duration of the opening of the injectors. If the engine does need more air then that fits in with the (slightly) improved starting when I depress the accelerator.

 

[Micky]

But is more air required at a cold start to raise the revs?

Yes, according to this:

http://www.autoshop101.com/forms/h60.pdf

The last bit looks interesting, using OBD-11 to command IACV positioning.

 

[Micky]

3' ambient this morning, it started first time. Still some hesitation though.

New IACV from Ford is £51, anyone know of an alternative supplier?

 

[jarhedch]

no, Ford is only place to get it, and the ICV does not always get 12V, it gets a duty cycle, meaning the ECM turns off and on power to the ICV very fast, producing a lower or higher voltage depending on what is needed. It shouldn't necessarily make a noise, E.G. warm starts and such, but i woujld defo suspect the ICV over anything else. I had an ICV that would work fine sometimes, and the be a pig to deal with for weeks(stalling at idle). Change it, you'd be surprised at the differnece.

 

[Micky]

Thanks jarhedch, no starting problems on Saturday, Sunday or Monday, a bit slow this morning which fits in with IACV problems. I'll see how it starts tomorrow. I'm just annoyed that I'll have to pay Ford £50 for something which should last the life of the car :angryfire:

I doubt if my multimeter would show pulse controlled operation!!

 

[jarhedch]

well, mine's started acting up again, and i've had it for less than a year. just goes to show how poor quality they are.

 

[Micky]

...and i've had it for less than a year .....

That can't be right, is the electrical signal to the device OK? I wonder if the valve is being contaminated by the oily fumes from the cambox breather. Perhaps an inline filter is needed?

I'm going to give my IACV one last chance and soak it overnight in meths, failing that it's £51 to Ford :BEEP: :BEEP:

 

[jarhedch]

signal's fine, idle is under sontrol 90% of the time, it just stalls once in a while, when it's needed more for finer idle control. The problem with my last one was a short circuit to ground once in a whiel that would go away and come back, it looks like this is the same thing again.

 

[Micky]

The meths helped for a few days, it also improved the IACV operation :laugh: still variable though, I also tried the "depress accelerator when you switch off" trick" (from this board?) That also seems to help, does the IACV open when the accelerator is floored? Although I don't like the idea of opening the injectors as the engine is being switching off.

Car runs well when it's hot, idle is rock solid. I'm loathe to pay Frod £51 for an IACV when it works (most of the time). Perhaps Frod will have a sale?

 

[jarhedch]

Don't bet on it, and there's nothing wrong with floring it and shutting the key off, as the ECM shuts down the injectors so there's no fuel flow. Doubt it would do any good though. bite the bullet, pay the moeny you'll be glad you did.

 

[James_McHattie]

Ive got a 1.4 Fiesta now, with the new Zetec engine - the manual says to let the revs drop to idle before switching off.

I guess the spark plugs turn off when the injectors do, and if your chamber is full of rich charge which hasnt been used it would condense on the cylinder walls. I suppose it might clear the oil from the bore wall overnight and cause a bit of wear the next day. But its only a guess.

If you put 12v across the IACV it should click. If it does then its fine. They are so easy to test that you might aswell bring a battery to a breakers and test them before buying one.

 

[Micky]

Don't bet on it, and there's nothing wrong with floring it and shutting the key off, as the ECM shuts down the injectors so there's no fuel flow. Doubt it would do any good though. bite the bullet, pay the moeny you'll be glad you did.

It's £51 worth of beer though, it's an intermittent fault at the moment, if it gets worse then it's no beer for me :sad:

 

[Micky]

If you put 12v across the IACV it should click. If it does then its fine. They are so easy to test that you might as well bring a battery to a breakers and test them before buying one.

It "clonks" when I test it (have a read of the early posts on this thread) but I've just realised that I test it removed from the inlet, perhaps it's binding when the securing bolts are done up?

£51 :sad:

 

[jarhedch]

If you put 12v across the IACV it should click. If it does then its fine. They are so easy to test that you might aswell bring a battery to a breakers and test them before buying one.

TBH, that means nothing. Mine clicked, but was still a problem, due to the fact that it required too much current to run due to a short in the thing and so the ECM could not control it properly. Buying a new one is really the best option.

 

[Bin_Man]

I changed mine recently and it certainly helped with hot idle problems. The valves are apparently a well known failure item and get gummed up by crap from the inlet side. You can sometimes clean them but in addition to soaking/sraying with carb cleaner, you do need to manipulate/aggitate the moving parts to free them up. Did bugger all good with mine, so I changed it. I'm sure it was only about £30 plus the vat from Frauds.

Whatever you do, replace the gaskit and check the mounting bolts - one of them was actaully missing on mine!

The other thing I'd try is blocking off the EGR. Piece of piss to do, the damn thing is completely unnecessary and they do fail. Pull the vacuum pipe off the solenoid on the bulkhead and stick a bolt in it. The best 5 minutes work you'll ever do. :L

 

[Micky]

The other thing I'd try is blocking off the EGR.

Is this on a Mk3? I have to logout to read car type, and then log back in to post. Is this a Firefox thing?

If the Mk3 petrol has an EGR, I'll try and block it rather than pay Frod the £51.

 

[Bin_Man]

Sorry, should have read your initial post more carefully! I don't know if the MK3 has an EGR. :beer:

 

[Micky]

I can't be arsed to pay Fraud £51 so I'm "managing" the IACV, most of my trips are 100 miles plus so the first few miles with hiccups isn't a big problem in the general scheme of things. Flooring the throttle when switching off usually means that cold starts are OK.