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Zetec Se Occasional Rev Hunting?


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#1 gavinh87

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Posted 28 April 2012 - 01:36 PM

Looking for a bit of help here guys, any help would be most appreciated
Focus mk1 facelift 2002 1.6 zetec se.
Not had this car long (3 weeks) and I have noticed my revs "hunt" occasionally its not much this is why I'm having trouble diagnosing the fault.
It does it after its been warmed up and i come to start it again the revs go up and down by about 100 rpm (not much I know) and if i leave it, it will do it all day long. But if i quickly blip the throttle it goes away and doesn't return.
I have been able to replicate this a few times by putting the both heated screens on and taking them back off, when the go off the revs begin to "bounce"

I have cleaned the idle control valve out twice (it didn't even look dirty when i did it) and I've cleaned the throttle body out (again really clean)
I found the PCV hose behind the inlet manifold to be collapsed I changed this but made no difference.
It might also be worth noting that when the revs begin "bouncing" it sounds like there is some sort of gurgle noise comes from where the airbox is but still does it when the airbox is removed.

I suspected a vacuum leak but after spraying every hose and gasket on the engine i can see with carb cleaner I dont think this is the case
I dont want to go round chucking parts at it if it's not 100% going to work I did this with my last car, spent £400 and still didnt fix the problem

Maybe MAP or MAF sensor? Although from what I have read those problems seem much more pronounced than what I have been experiencing
Also it drives perfect, no hesitation or misfire etc just idle problems.

Again thanks to anyone that takes time to read this lengthy post

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#2 gavinh87

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Posted 28 April 2012 - 05:45 PM

Little update, just been out on a run and did the instrument cluster test. Revs are near enough bang on 700 ( i couldnt get it to hunt, typical)
Also the battery voltage seemed a bit off, with engine off it was reporting 11.4v and when driving it was reporting 14.1 and with full load on engine at idle the voltage reported 11.7v.
These figures suggest my battery is dying, has anyone ever heard of a low battery causing a car to hunt?

#3 STEADS

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Posted 28 April 2012 - 06:40 PM

My son had a similar problem on his at the back of the inlet manifold you will see two white vacuum blanking caps on my sons car these had come adrift (appear to be non rewnewable) we could hear it hissing manged to tape them up (reseal) and has cured the problem its worth a look.



#4 gavinh87

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Posted 28 April 2012 - 09:52 PM

I too can hear a hissing noise but cant find a leak.... Was your sons inlet at the front of his engine? I have tried looking but cannot see these blanking caps. Dont suppose you have any pics??

Posted Image
This is where the hissing appears to be coming from, (not my pic) have sprayed carb cleaner around there but didn't appear to be any change in engine revs
Thanks for replying.

#5 STEADS

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Posted 29 April 2012 - 09:27 AM

Your engine is a different configuration to my sons his in let is at the back as you state but i would say if you can pin down that hissing thats where your problem lies might even be that a vacuum hose has slipped off the pipe in the picture i think is the brake servo pipe and that valve like thing on it is possiblev a non return valve possibly the fault i,m sure i,ve read on either this forum or another these can go causing the problem you state when we bought my sons engine we had to purchase one from fords not that expensive hope this helps

#6 gavinh87

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Posted 29 April 2012 - 10:40 AM

Thanks for your input STEADS, the leak would appear to come from the idle control valve or the throttle body but ive had both of these off and put gasket sealant on and its still the same. Maybe I'll have to go deeper or get a garage to smoke test it.

#7 gavinh87

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Posted 30 April 2012 - 08:02 PM

Another update, was pulling out of a junction today and it was jerking in 1st and 2nd gear at low revs too I wasnt giving it the beans.
I pulled over turned engine off, restarted and it was fine. Got home from work and decided I'm going to have another go at this.
I found the hissing noise to be coming from the fuel regulator and/or the fuel return pipe with those stupid quick release clips (these are a nightmare to get off!)
I'm going to the dealers tomorrow to replace these parts, I will keep you updated.

#8 gavinh87

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Posted 01 May 2012 - 05:14 PM

Another update (getting a bit bored now tbh lol) replaced the fuel pressure regulator and the fuel line and the hissing has gone :)
The erratic revs happened when i was waiting for the Mrs to come out of the asda I moved the steering wheel about an inch and that was it, the revs wouldn't stop bouncing until i blipped the throttle.

It does seem to drive better now and the idle until it starts hunting sounds a lot better.
Anyone want to shed any opinions on this? Ive also noticed that when coming to a stop from 30mph it seems like it wants to stall, it never does and the revs do recover but it feels weird. Also need to resolve the the gurgling noise from the engine bay.

#9 vince9740

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Posted 01 May 2012 - 07:33 PM

I bought a Focus 1.6 LX 2002 in March this year and it had the same type of symptoms as yours, thankfully I had mine fixed, so this may be of some help to you... When I test drove the car it was ok. I asked for a Cam belt replacement as a part of the sale which they did, and the mechanic had to fit a new cam positioning sensor as well. On taking the car away, I noticed when coming up to junctions/traffic lights the revs would be a bit too low, then come back up a bit but keep on hunting, never flattening out. Once, it actually stalled coming up to a junction. Also, on the first drive which was in the dark, the headlights and interior lights were flucuating as if the battery was running out. I took it back to the dealer who got in touch with a Ford garage. I was told to take it into them, and they cleaned out the Idle Control Valve, as well as updating the software on the car. I don't know why the cam belt replacement/cam positioning sensors would have anything to do with it, but it started happening after this was replaced. Anyway, after going to Ford its now fine, so maybe this could be a solution?

#10 gavinh87

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Posted 02 May 2012 - 06:51 PM

Thanks for the input vince9740, my car was jerking again today in 1st and 2nd gear.
My obd scanner came today I connected it up and took it for a drive, all live data looked fine oxygen sensor, MAP, fuel trims look fine and there were no codes stored in the ECU. I was thinking idle control valve at first but it does it when accelerating and as far as i know it only plays a part at idle? I then thought coil pack but wouldnt it do it all the time?
I'm going back to basics and I'm going to try changing the fuel and air filters the weekend.

#11 gavinh87

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Posted 04 May 2012 - 10:07 PM

Another update, drove it last night with my scanner on it was bucking and jerking really bad and registered nearly 300 misfires in around 20 mins :/ I changed the leads and coil pack today with a decent not cheapo set and all seems fine so far. Gonna keep my fingers crossed and will keep you updated.

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