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Discussion Starter #1
I have a 2004 Focus SE Zetec auto with 141,000 miles that has just started stumbling with air on, in gear at a stop. Car idles fine without air on in gear with brake on. It runs perfect at anything over an idle with air on or off.

Have checked for collapsed or leaking hoses as suggested by others. The fact that it idles fine without air on is confusing and that it only stumbles to point of feeling like it will die with air on in gear at stop is confusing. After releasing brakes and getting past idle it runs fine

No codes have been thrown.

Could it be the IAC valve? I thought if it goes bad it would idle fast or slow all the time.

thanks for any help
 

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Grey Friar
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It's been a long time since I had my Zetec, but IIRC... dirty MAFS, clogging air filter, dirty injectors, DPFE starting to go bad (not enough to throw a code yet), FRP sensor going bad, or the most often... PCV hose behind the IM, at the bend that Ford armored in replacement parts, gets mushy and leaks a bit, but you can't see a hole.
 

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Discussion Starter #3
It's been a long time since I had my Zetec, but IIRC... dirty MAFS, clogging air filter, dirty injectors, DPFE starting to go bad (not enough to throw a code yet), FRP sensor going bad, or the most often... PCV hose behind the IM, at the bend that Ford armored in replacement parts, gets mushy and leaks a bit, but you can't see a hole.
Thanks for quick reply. I “squished” the PCV to test for softness and checked air filter when I had box out to repair those useless retaining bolts. Also checked and cleaned MAF. Car gets right at 29 mpg on highway and just under 26mpg with air on - if that helps.
I will order new PVC hose as that is what I suspected too as I am seeing oil under IM but valve cover is dry so I suspect a hole that I can’t see without having it off or hear a leak.
New symptom today - it started dying in park when air kicks on.
Don’t have a tach but will use dash hack to get to tach to watch rpms.
Thanks
 

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Grey Friar
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A can of B-12 in a half full tank will do a bit of injector cleaning, too. There are other things less typical (spark related)... anyway, you should check/clean/improve all 5 grounds while you're at it, but wait until you change the hose to go further. Good luck.
 

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I would check the ignition coilpack - especially if it is older. They develop hairlibe cracks in the housing and can cause the symtoms you are seeing. Very common issue on Zetec. My 02 had a bad coilpack and would idle fine and no CEL. Four bolts to remove for inspection. Also look at the harness connector for disintegration of the connector housing and/or wire insulation.

Good luck
Paul
 

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Already been through that...............it's older engine with ring wear and shows beginning around 120K miles on a lot of them. The engine balks at a/c coming on because the idle speed bump up at IAC takes a fraction of a second to happen.

You must have the full amount of idle air for one, that means PCV valve must be fully open and not clogged and the TB butterfly must be clean on the edges too. Past that, the IACs are normally set to bump UP the idle, you readjust the TB butterfly to make them have to bump it back down instead and helps greatly but very touchy to do.

Normal PCM controlled idle speed warm is around 730-750 rpm, when you turn on a/c it drops but a new motor powers right through that and the idle really doesn't drop at all. An older one with less ring seal will though and then the almost-a-die happens. It happens while the IAC is responding, that does not happen instantaneously.

Get the engine good and warm and then disconnect the IAC harness to get the real idle speed at the TB butterfly setting. It should drop a bit. You need to bump that up to where the idle is around 800-850ish using the idle speed setscrew in the TB. Then connect the IAC back up and instead of idling up it will be taking some out to drop DOWN to 750, that extra overhead will at least help the dying issue, it pretty much made the problem go away on mine. It works because you end up with the TB slightly open more than it was before and that helps. Older engines always like the TB to be open a bit more to keep them idling, they do not produce the vacuum draw a new one does so they need slightly more air to make up for it.

That setting is touchy, I bumped the setscrew maybe 1/8 turn total, if you go too far the idle may begin to hang high, and then back it down part of that.

The engines make maybe 10-15 hp. at idle rollover, when you suddenly load that with the extra 3-4 of a/c coming on an older engine chokes for a fractional second until it recovers, a newer one makes enough torque to roll right through that like it was nothing.
 

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Discussion Starter #7
I want to thank all that replied or will still reply for all the great suggestions.

I am going to check all of them when it cools off - it’s 93 with heat index of 109 where I live so the air in house beats out air in car.

I did brave the heat long enough to pull air intake hose off of TB and opened/closed the butterfly and it seemed to catch and edges were rather black and the one I could get my finger on was rough with carbon. I carefully cleaned with throttle body/choke cleaner and used dash hack to get to tach and started it. Went to about 1250+/- and then backed down to around 800/850 after a few seconds and when I turned air on it dropped to between 700 and 750 and never stumbled or died. Granted I only drove it for about 6 miles with lots of staring stopping but it stayed at the 700/750 with air on. Engine even “sounds” better - maybe wishful thinking.

Am going to check all the other suggestions as soon as I can. I have ordered the PCV hose just because it is a known problem as well as checking the coil pack since it is also a known problem.

Will check back with results so maybe it will help someone else with a similar problem.
 

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It doesn't take much to mess up the TB aircrack, they need to be kept clean and I do mine maybe every couple years, it helps starting without touching the gas pedal a lot.

Maybe save the money on coil. The coils ARE a well known problem and you change them like airfilters on these but they will not produce a problem as specific as yours is now. Or, the problem at every time the a/c is on and the engine is good and hot, and only showing at idle. The coil cannot pick that specific a set of circumstances to act up, it will do it with no timing or whatever when it decides to go. The hairline crack check all over it in bright sunlight is the best way to find one bad. The harness connector can go bad where it disappears inside the coil too and sometimes not seen. The harness is too tight dropping down from the MAF and the tautness then cracks the wires, Ford trying to save pennies on copper there. The quick to biodegrade wire insulation adds to the problem there too by breaking too easy.
 

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BTW a worn TPS can possibly add to that issue, they wear typically the most at idle and then wear at the carbon track can make for erratic idle that sometimes tries to die.

Be aware that if you need one there is none for the automatic trans, you have to swap to a later '03 throttle body to get the TPS. The parts stores will swear they can still get the TPS but then they give you the manual trans one, which IS different but you can't see it by eye. The clocking being off by like 5 degrees to make the car idle weird and shifts get very hard. There IS a workaround to prevent having to buy the entire TB over again just to get the TPS.
 

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Discussion Starter #10
BTW a worn TPS can possibly add to that issue, they wear typically the most at idle and then wear at the carbon track can make for erratic idle that sometimes tries to die.

Be aware that if you need one there is none for the automatic trans, you have to swap to a later '03 throttle body to get the TPS. The parts stores will swear they can still get the TPS but then they give you the manual trans one, which IS different but you can't see it by eye. The clocking being off by like 5 degrees to make the car idle weird and shifts get very hard. There IS a workaround to prevent having to buy the entire TB over again just to get the TPS.
Thanks for the replies. I have to make a trip today of about 160 miles and it is going to be hot and humid again today - 108 heat index - so it will be a good test of the cleaning of the butterfly.

Thanks to everyone who responded with great suggestions. Will try one thing at a time to hopefully verify which one fixed it then I will post back what did it.
 

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Grey Friar
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Good it works, so far. Nice that it was just a dirty TB plate edge... kudos to AMC for sniffing that out (even if there might be a tiny air leak still to be discovered). All suggestions/education are good and possibles, except for adjusting the TB set screw... a guy, like AMC, with enough experience and patience can get away with it, but it is more likely to add another idle problem that is off-book. Leave that alone... old school mechanics who recall adjusting carbs may be okay about trying that, but the teeny tiny bit's of turn needed to create dramatic effects on a ECM engine, make that something you do as a last resort... desperation move.

Hope the trip works out.
 

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While I constantly advocate never touching the TB butterfly setting, as it gets you lost in the IAC pintle travel, at some point you may be forced to. How I found out exactly what happens when you mess with it. One other effect that shows you pretty quick where you are at with it is that the engine braking will radically change, and it was welcome in my case as I had always thought the car threw away extra mileage as it engine braked too much even at 65 mph and a throttle rolloff, it felt like the brake was being dragged slightly on. The TB adjust fixed that too.
 
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I want to thank all that replied or will still reply for all the great suggestions.

I am going to check all of them when it cools off - it’s 93 with heat index of 109 where I live so the air in house beats out air in car.

I did brave the heat long enough to pull air intake hose off of TB and opened/closed the butterfly and it seemed to catch and edges were rather black and the one I could get my finger on was rough with carbon. I carefully cleaned with throttle body/choke cleaner and used dash hack to get to tach and started it. Went to about 1250+/- and then backed down to around 800/850 after a few seconds and when I turned air on it dropped to between 700 and 750 and never stumbled or died. Granted I only drove it for about 6 miles with lots of staring stopping but it stayed at the 700/750 with air on. Engine even “sounds” better - maybe wishful thinking.

Am going to check all the other suggestions as soon as I can. I have ordered the PCV hose just because it is a known problem as well as checking the coil pack since it is also a known problem.

Will check back with results so maybe it will help someone else with a similar problem.
Screamin Demon Coil Live Wire set plugs (MSDignition or PerformanceDistributors / Steeda)
Had for last 15yrs best performance for Northern New Jersey for 240k 02 Zetec ZX5 Twilight blue
 

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Discussion Starter #14
Sorry for late reply - after cleaning TB I thought I had it as idle smoothed out and on first drive it worked fine with no stumble. After my 160 mile trip the stumble was back. So I changed PCV hose from steel tube to intake. The old hose was factory and I found no holes but elbow was very soft so I thought I had found it. Nope. It still has the stumble at idle in gear with brakes on and air on.
Am thinking IAC but would that only show problems with air on? Wouldn’t it show up all the time? I did the dash hack to watch rpm and when air kicks in the idle will drop to 500 or so for a second and then usually recover to about 750/800 rpm. Sometimes it drops lower and that is when it almost dies.
Air filter is new. MAFS has never been changed but is clean. Still no codes thrown. .
Could coil be causing this strange problem? I used to be a ford mechanic back in the 70’s/80’s when you could open hood and still see the ground and electronics were not near as complicated as today and I hated just swapping expensive parts and still think that way now.

Any thoughts?
 

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Discussion Starter #17
Paul - you were right. No hairline cracks but big one width of coil pack on 1/4 side which is towards engine. On closer inspection after cleaning found several more large cracks on other side too. Wonder it was running as well as it was

GREAT advice. Thank you
 

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Awesome! Check that wiring harness too...I've replaced it on all three of my Foci because it had tiny cracks in the insulation that were causing random misfires.
 

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Discussion Starter #19
Awesome! Check that wiring harness too...I've replaced it on all three of my Foci because it had tiny cracks in the insulation that were causing random misfires.
I checked that right after I took it off because several other suggested it coul be a problem.
They are delivering new coil pack so haven’t actually 100% proved that was it but with all the hairline cracks and then the huge one going width of pack and after good cleaning that crack extends down to almost the base it has to be problem. I would be shocked if it isn’t just like I’m shocked it still ran so well.
Great advice here. Really appreciate it.
 

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Discussion Starter #20
6D036B28-F457-4E30-A05E-61B7DBCD8F2A.jpeg
That was the problem. Other side had smaller cracks.
Great advice here. Thank you all.
 
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