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Engine Revving Up And Down


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#1 david295

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Posted 23 August 2012 - 08:14 PM

MK 1 1.6 16 zetec

If i leave car on tick over and switch on headlights, the revs go up and down on there own.

Would i be right in thinking idle control valve.

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#2 artscot79

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Posted 23 August 2012 - 08:17 PM

not necessarily it could be an alternator fault or an air leak in a vacum hose

#3 gc88

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Posted 24 August 2012 - 09:32 AM

How much are we talking here? How much do thry fluctuate by?

#4 david295

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Posted 24 August 2012 - 10:20 AM

Between the o and 1 or rev counter, there are 2 black lines, normally mine ticks over at the first line under the one.

If i switch on headlights it drops down to the first line just above zero, then jumps up to next one under 1, and just fluctuate's between them 2.

#5 gc88

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Posted 24 August 2012 - 01:04 PM

Surely thats just the engine coping and managing with the extra load?

I'm no expert tho..

#6 david295

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Posted 24 August 2012 - 01:46 PM

Its not normal, it actually sounds like someone is pressing allcelerator pedal (excuse spelling) thats how much of a change there is in engine speed.

#7 jeebowhite

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Posted 24 August 2012 - 01:47 PM

as arts said, we cant rule out an alternator pumping the wrong voltage, but it could be anything as simple as the ICV needs cleaning and or replacing, or the air filter could do with being replaced. does it only happen with the headlights on?

if you have no electrics on but the engine runs, does it idle rough?
If you then switch on any other electrics (one at a time) does anything else affect it?

Once you have checked these it will help further...

#8 artscot79

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Posted 24 August 2012 - 02:04 PM

do the dash trick and go to engine rpm take a note of the speed then switch the lights on again and note the speed now the idle speed at idle with no electrics should be between 670-730 with a warm engine so first thing is to make sure that is what you are getting as the rev counter doesnt give exact figures it sits at 800 but the car doesnt idle at 800rpm

next switch on the lights and watch the dash readout the rpm should increase sometimes to about 800rpm then it should drop and settle it will fluctuate slightly but it should still be around 670-750rpm no higher on a warm engine note the figures now on the dash test go to battery voltage and see what it says i would expect it to be 14.1-14.3v with the engine running and lights off switch on the lights and watch the voltage it should go down then instantly back up to 14.1-14.3v again note the figures and post them up here if the revs when the lights are switched on go high and stay high for more than a second it indicates the idle control valve disconnecting the connector to the icv will show if the engine stays the same no increase or decrase in revs the icv is knackered if the revs do change its no the icv thats at fault but maybe a split or collapsed hose and blocked pcv valve

#9 david295

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Posted 25 August 2012 - 09:11 AM

as arts said, we cant rule out an alternator pumping the wrong voltage, but it could be anything as simple as the ICV needs cleaning and or replacing, or the air filter could do with being replaced. does it only happen with the headlights on?

if you have no electrics on but the engine runs, does it idle rough?
If you then switch on any other electrics (one at a time) does anything else affect it?

Once you have checked these it will help further...

Icv has been cleaned, air filter new, it happens with anything elctrical turned on.
Engine runs perfect on tick over with nothing switched on.
I have been told that I should have a 105amp alt, but the new one i have which is a bosch recon, is only 80amp, the haynes manual states 80amp.
Whould it matter if i put a 105 amp one on

#10 david295

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Posted 25 August 2012 - 09:12 AM

do the dash trick and go to engine rpm take a note of the speed then switch the lights on again and note the speed now the idle speed at idle with no electrics should be between 670-730 with a warm engine so first thing is to make sure that is what you are getting as the rev counter doesnt give exact figures it sits at 800 but the car doesnt idle at 800rpm

next switch on the lights and watch the dash readout the rpm should increase sometimes to about 800rpm then it should drop and settle it will fluctuate slightly but it should still be around 670-750rpm no higher on a warm engine note the figures now on the dash test go to battery voltage and see what it says i would expect it to be 14.1-14.3v with the engine running and lights off switch on the lights and watch the voltage it should go down then instantly back up to 14.1-14.3v again note the figures and post them up here if the revs when the lights are switched on go high and stay high for more than a second it indicates the idle control valve disconnecting the connector to the icv will show if the engine stays the same no increase or decrase in revs the icv is knackered if the revs do change its no the icv thats at fault but maybe a split or collapsed hose and blocked pcv valve

Mine does not show the engine revs on the dash trick, it doesent even show speed, if i disconnect icv on tick over engine speed does drop, but yet again, if i disconnect alt completly, that is red power cable and 3 pin smart charge plug, i can turn on everything elctrical, and there is no change in engine speed, everything works perfect, if i start enging and run it off just battery and no alt

#11 artscot79

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Posted 25 August 2012 - 02:24 PM

all fords show this info using the dash trick mate if your car doesnt you have far bigger issues icv fine there wont be a change in engine speed if you disconnect the alt its not connected so theres no load on it to make the revs drop in the dash menu using the dash trick you will get the info required engine off press and hold trip reset and switch engine on with the reset still pressed it will say test release trip reset each press scrolls through the menu.

#12 STEADS

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Posted 26 August 2012 - 09:27 AM

On my sons 1.8 focus same year as yours at the back of the inlet manifold there are two white vacuum blanking caps (non renewable ) these had come adrift and caused an air leak taped them up and cured the problem might be worth a look to see if this is the same problem on yours .

#13 jeebowhite

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Posted 28 August 2012 - 01:53 PM

the 110 is the ideal output because the focus uses a smartcharge gem system which is going to ensure your car copes more appropriately. so it would be better if you could get the right output.

With regards to the dash trick, its been a while since I used it, but there should be an option on there as your scrolling to see the RPM in realtime as digits as well as dash... if you have a look at the "dashboard trick" thread at the top of the focus forum, that has a step by step of the entire self diagnostics...

#14 david295

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Posted 29 August 2012 - 08:07 AM

the 110 is the ideal output because the focus uses a smartcharge gem system which is going to ensure your car copes more appropriately. so it would be better if you could get the right output.

I believe it has the correct output 80amp alt, thats what is mentioned in haynes, the 110 is for diesels.
It has been to fords for a scan, and they say no fault, they say its normal for revs to drop when brake lights come on.
Now I do not agree, i have never had a car that does that

#15 artscot79

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Posted 29 August 2012 - 09:23 AM

revs do drop when the brakes are applied if you watch the revs on the dash trick and switch on electrics or press the brakes the revs and battery voltage momentarily drops on most cars you dont notice its because most cars idle at 800-850rpm the foci idles low at 670-730 for emission purposes so what they say is true and they all do it all of them

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