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Idle Tick Over Problem


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#1 greggp

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Posted 02 November 2010 - 08:57 PM

have a 2008 Focus titanium 1.8 petrol and today something really strange happened. The car has recently had its 2nd service done 20k.

I was in stop start traffic for around 50 minutes (rush hour) this evening and suddenly my car started idling funny - it almost cut out and battery light flicked on - I gave it more revs and then eventually the problem seemed to go away. It was idling normal throughout the traffic jam at approx 750rpm then all of a sudden the revs shot up and then dropped really low and almost cut out! I have ready on other web pages issues with idle control valves etc - Could this be the cause?

Prior to this problem I have noticed that if ever I coast in neutral the revs do fluctuate up and down - thought this was normal so never raised any concerns before but now I think this could all be related.

Any help or advice appreciated
thanks

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#2 artscot79

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Posted 02 November 2010 - 09:46 PM

have a 2008 Focus titanium 1.8 petrol and today something really strange happened. The car has recently had its 2nd service done 20k.

I was in stop start traffic for around 50 minutes (rush hour) this evening and suddenly my car started idling funny - it almost cut out and battery light flicked on - I gave it more revs and then eventually the problem seemed to go away. It was idling normal throughout the traffic jam at approx 750rpm then all of a sudden the revs shot up and then dropped really low and almost cut out! I have ready on other web pages issues with idle control valves etc - Could this be the cause?

Prior to this problem I have noticed that if ever I coast in neutral the revs do fluctuate up and down - thought this was normal so never raised any concerns before but now I think this could all be related.

Any help or advice appreciated
thanks


its possible its the idle control valve and yes( although you shouldnt be coasting as it can damage the engine and saves no fuel as the injectors still inject the fuel to run at that speed) the revs shouldnt fluctuate take it back to get it checked out ide be surprised if its the icv so soon but it is possible it could also be the vss vehicle speed sensor or even the head temperature sensor best bet is have it hooked up to diagnostics and get it checked out and stop coasting it will cause gearbox and engine damage

#3 greggp

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Posted 02 November 2010 - 09:59 PM

its possible its the idle control valve and yes( although you shouldnt be coasting as it can damage the engine and saves no fuel as the injectors still inject the fuel to run at that speed) the revs shouldnt fluctuate take it back to get it checked out ide be surprised if its the icv so soon but it is possible it could also be the vss vehicle speed sensor or even the head temperature sensor best bet is have it hooked up to diagnostics and get it checked out and stop coasting it will cause gearbox and engine damage


Many thanks for your comments and help. do you think I will be covered on ford warranty?

#4 catch

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Posted 02 November 2010 - 10:36 PM

Many thanks for your comments and help. do you think I will be covered on ford warranty?

If you have had it serviced to the Ford service schedule, then I don't see why not. Otherwise the three year warranty is not worth the paper it is written on.

#5 mjt

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Posted 03 November 2010 - 09:40 AM

you shouldnt be coasting as it can damage the engine and saves no fuel as the injectors still inject the fuel to run at that speed

The injectors can't be controlled by road speed can they? Surely they are controlled by data from the mass air flow sensor and engine speed measured from the crankshaft position sensor? If they were controlled by the VSS output what happens when you're in different gears?

#6 artscot79

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Posted 03 November 2010 - 01:20 PM

The injectors can't be controlled by road speed can they? Surely they are controlled by data from the mass air flow sensor and engine speed measured from the crankshaft position sensor? If they were controlled by the VSS output what happens when you're in different gears?


put it this way when you coast does the engine die? it doesnt because fuel is still being pumped through the injectors to the engine the same amount of fuel to maintain that speed as when you woulkd be in gear the system is all interconnected the vss sensor crankshaft sensor head temp sensor etc etc the point is as the cars moving the fuels still being pumped the vss doesnt control them but is part of the process which is why cars with faulty vss can actually cut out while driving at say 30mph

#7 mjt

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Posted 03 November 2010 - 03:27 PM

Of course the ECU uses other sensors apart from the ones I mentioned. One thing I forgot to mention is that the fuelling is closed-loop, the fuel delivery being controlled by feedback from the oxygen sensors in the exhaust system to minimise emissions, so I don't see how it can overfuel whilst you're coasting. I know that Haynes is not the be-all and end-all so-to-speak when it comes to accuracy but from their description of the fuel system it appears that the VSS signal is used by the ECU to control fuel shut-off on the overrun, when the engine speed is faster than what is being demanded by the throttle sensor. A faulty VSS would therefore be most likely to cause incorrect fuelling under this condition which may be why it affects normal running. Once you declutch the engine speed falls back to tickover at which point this no longer applies and the fuelling will be controlled by all the other sensors.

At least, that's how it appears to me. Maybe someone with a better technical knowledge of fuel systems can give a definitive answer.

#8 greggp

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Posted 03 November 2010 - 03:41 PM

it wanted to cut out last night when I engaged neutral to coast - battery light flashed but I quickly engaged gear and it kept running.

#9 lucas1787

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Posted 03 November 2010 - 04:54 PM

it wanted to cut out last night when I engaged neutral to coast - battery light flashed but I quickly engaged gear and it kept running.

Had the same problem with mine the other week,put a new idle control valve on and was still the same.After some investigation,I found a breather hose split coming of the engine.Replaced and is now running fine.

#10 artscot79

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Posted 03 November 2010 - 09:20 PM

Had the same problem with mine the other week,put a new idle control valve on and was still the same.After some investigation,I found a breather hose split coming of the engine.Replaced and is now running fine.


sounds like the vss then get it into ford and have it checked out while its under warranty

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