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Discussion Starter #1
caution be ready to read....Alright I'm looking for everyone's opinion on what my problem might be with my svt since everyone on here has experience with different situations.

Ok, my car will stumble at idle when i push in the clutch and coast to a stop light. By stumble i mean the idle will drop to 500rpm or less then rev up to 1000 and keep going back and forth, after about 30 seconds it may finally settle down. This only seems to happen when I have the A/C on and actually the car has died twice on me before from this but it started right back up. Today was especially bad because i had the A/C on and my headlights on (it was dark this morning!) and everytime i pushed the clutch in it really stumbled, I was quite concerned it was gonna die on my way to work.

Here's the the thing, when i drive with the a/c off everytime it comes to idle it is absolutely fine no stumbling what so ever!

Please help me out fellow focus fanatics! I have all weekend to poke around under the hood to fix this.
 

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stumble?

Check all your vacuum lines! I had the same issue with my svt. I ended up having a hole in the lines going to the solenoid valve on the pass rear of engine compartment. they were rubbing themselves and made a hole. Solved all stumbling for me. later.
 

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Discussion Starter #4
Sounds like a good place to start. I was hoping it wouldn't be anything electrical like a bad alternator or a bad ground somewhere.
I will post an update when I find the problem!
thanks again
 

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is the ac blow warm when at idle then cold when driving? if so i have this same problem
 

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ok.. so unfortunately I have the same problem and my buddy who owns an svt also gets this from time to time.. mine does it quite frequently.. the only piece of information i have for u is that when i bought my car from the previous owner he told me that the only thing he had replaced was a part in the "transmission" (dont know if he was right) that went bad causing the car to idle improperly on starts and stops.. I figure that on my car this part went bad again.. it is not the alternator or battery tho because i just had both of those replaced and my car still does it.. so dont waste your money on either of them.. I cant tell u exactly what it is but hopefully this might lead u in the right direction.. i personally dont care because my car always starts right back up.. if u find out what it is let me know!
 

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Discussion Starter #7
Ok so I checked my vacuum lines and didn't see any holes. I did find a rub spot on what I believe is the pcv hose so I taped around just in case. Can someone confirm its the pcv hose? it runs from a spot under the header and the over the top of the transmission where it leads to the back of the engine

Also this weekend I clead up all the grounds connecting to the chasis by the battery, all just for the heck of it.

So its been really hot and humid here and I have been driving around with the a/c on and sure enough the problem has not gone away. Clearly I'm not the only one with this issue. Are ther any other things I should check out?
I'm thinking it might be possible that one of the vacuum hoses is collapsing when at idle w/ the a/c on?
 

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Discussion Starter #8
is the ac blow warm when at idle then cold when driving? if so i have this same problem
You know it actually doesn't feel as cold at idle as it does when i'm driving. But I don't know if that relates to the stumbling issue or not????
 

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I have the dropping below normal idle, too. I'd add; when clutching it drops not only lower than normal but FASTER as well. Also slower throttle response and slower acceleration.

IT'S BEHAVING LIKE A VACUUM LEAK...go figure.

I was checking and found the valve cover gasket(s) leak a small amount of oil - I also had to change back to the correct spark plugs and not the NGK. They are too hot for SVT BUT did not show any evidence incorrect mixture (ECU should compensate so I'm not surprised.) Oddly enough the plugs helped a bit. I still have not found a vacuum leak but I'll keep looking.

The A/C is still blowing cold but really seems to reduce power output more than normal under the 'vacuum leak' conditions.
 

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Discussion Starter #10
It's possible there is a pin hole in the the intake manifold rubber connectors. I still haven't solved this problem. I'm to the point where i'm just going to start replacing all vacuum hoses one at a time till the issue is solved...
 

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It could be a vacuum leak. What do your couplers look like? Also, if its only doing it with the a/c on and at idle, that would increase load on the engine and it may stumble more from a smaller vacuum leak. Check your STFT if you can, that'll tell you if you have a vacuum leak or not. you could take your throttle body off and clean it up real good with some TB friendly cleaner. I'd say have your a/c checked out. Is your compressor cycling on and off when its happening?
 

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Discussion Starter #12
My intake couplers look a little grimey, kind of a light oily gritty coating on em. I'm thinking its a small hole because like you said it only occurs with the increased load on the engine.
The a/c seems to run fine it stays nice and cold in the car, I had fog form on the outside of the windows on a humid morning.
Could you please elaborate on what the STFT is?
Thanks
 

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Well for one thing if the couplers look all Grimey and weak, just start there. I'd get the cfm couplers. They're a lot stronger than the factory ones.

STFT is the amount of fuel the ecu is adding or taking away to maintain a desired fuel mixture.

When you view these (via a scan tool/flashing device) It can tell you when something is "out of whack" such as if you had a vacuum leak, your stft will probably read A positive %, I.E. The ecu would be adding more fuel to compensate for a lean condition.
 

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... I also had to change back to the correct spark plugs and not the NGK. They are too hot for SVT BUT did not show any evidence incorrect mixture (ECU should compensate so I'm not surprised.) Oddly enough the plugs helped a bit. I still have not found a vacuum leak but I'll keep looking.

The A/C is still blowing cold but really seems to reduce power output more than normal under the 'vacuum leak' conditions.
You can't see the damage as it pits the valves, which leads to sealing problems at low rpms ...

It's why I made the spark plug thread over on F/J [ninja]
 

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Discussion Starter #15
Sounds like the couplers are a good place to start. Once I get them and install them I will report back if it fixes the stumbling problem.
 

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You can also mist water around possible leaks. Once you mist and the engine idles smooth (water temporarily plugging small holes) you have found your leak.
 

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I've experienced similar issues with idle dips and intermittent stalling during dashpot (return to idle) that were related to the front 02 sensor. This condition was MUCH more frequent in hot weather, also. I was setting an intermittent slow response code (P0141) but since I was able to draw the 02 signal quickly rich with carb spray and quickly lean with a vac leak I assumed it was an engine management issue or even a small vacuum leak NOT a lazy 02.

After looking at my Long Term Fuel Trims at idle I concluded that I didn't have a vac leak. A vac leak will make the PCM learn a new long term fuel adjustment value that is significantly positive (+10% or more, usually). My trims were very close to zero. Fordtech is incorrect that the STFT values would likely be a bit positive. Initially, yes - they would indicate an immediate need for additional fuel. But, as this need for additional fuel continues for any amount of time, the PCM will simply apply this strategy to the adaptive fuel tables in the form of a LTFT. The PCM wants to keep the STFT hovering a few % above and below zero to make the 02 signal switch. The LTFT value represents what the PCM has learned it needs to do with fuel adjustment to maintain stoich.

The reason I think some of you with this issue may be dealing with an 02 issue and not a vacuum leak is the frequency at which these vehicles tend to go through 02 sensors. I don't know if it's the location of the sensor or what but the SVTF's have a reputation for killing upstream o2 sensors. Most people experience their failure in the form of a CEL, but the PCM only has to turn on the light if the lack of upstream 02 switching frequency exceeds 1.5 times the emissions standards. In other words, the light will only come on if there is a relatively severe issue.

My 02 was bad enough to cause the engine to stall while in Closed Loop as the PCM added and took away fuel attempting to get it to switch......but good enough to switch within the allowable OBD compliance perameters.

I replaced the sensor and my issues immediately went away.


Of course, I curbed the damn thing two weeks later and bent the sensor so now I've got another bad 02 and a blown fuse for the heaters, lol but that's just how my life works.....[hihi]


Either way, I see a lot of people tracking down suspected vacuum leaks with arguably not-the-most-convenient-or-effective ways and figured I'd share my experience. G/L
 

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Discussion Starter #18
I've experienced similar issues with idle dips and intermittent stalling during dashpot (return to idle) that were related to the front 02 sensor. This condition was MUCH more frequent in hot weather, also. I was setting an intermittent slow response code (P0141) but since I was able to draw the 02 signal quickly rich with carb spray and quickly lean with a vac leak I assumed it was an engine management issue or even a small vacuum leak NOT a lazy 02.

After looking at my Long Term Fuel Trims at idle I concluded that I didn't have a vac leak. A vac leak will make the PCM learn a new long term fuel adjustment value that is significantly positive (+10% or more, usually). My trims were very close to zero. Fordtech is incorrect that the STFT values would likely be a bit positive. Initially, yes - they would indicate an immediate need for additional fuel. But, as this need for additional fuel continues for any amount of time, the PCM will simply apply this strategy to the adaptive fuel tables in the form of a LTFT. The PCM wants to keep the STFT hovering a few % above and below zero to make the 02 signal switch. The LTFT value represents what the PCM has learned it needs to do with fuel adjustment to maintain stoich.

The reason I think some of you with this issue may be dealing with an 02 issue and not a vacuum leak is the frequency at which these vehicles tend to go through 02 sensors. I don't know if it's the location of the sensor or what but the SVTF's have a reputation for killing upstream o2 sensors. Most people experience their failure in the form of a CEL, but the PCM only has to turn on the light if the lack of upstream 02 switching frequency exceeds 1.5 times the emissions standards. In other words, the light will only come on if there is a relatively severe issue.

My 02 was bad enough to cause the engine to stall while in Closed Loop as the PCM added and took away fuel attempting to get it to switch......but good enough to switch within the allowable OBD compliance perameters.

I replaced the sensor and my issues immediately went away.


Of course, I curbed the damn thing two weeks later and bent the sensor so now I've got another bad 02 and a blown fuse for the heaters, lol but that's just how my life works.....[hihi]


Either way, I see a lot of people tracking down suspected vacuum leaks with arguably not-the-most-convenient-or-effective ways and figured I'd share my experience. G/L
Thanks for sharing your experience. Everything you have stated sounds completely logical as to why I would have these idle issues, I will look into replacing the O2 as well!
 

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I had a similar issue. My o2 sensor under the car on the bottem by the cat was going and then eventually went. I would be in nutral and going to come to a stop at a light and it would idol horrible and stall out most of the time, sometimes if I cought it in time I could reve, it up and it would fix it self. It was o2 sensor 2, it was really weird, but with all the salt and crap up here in N.y., it made sense that it would go. Lots of possibilities, and my car also with the a.c. on has a huge power loss and crazy idoling. This is normal for a 4 cylinder motor. Especially when you are starting off in first do you have the car almost die when the air is on and you don't almost like pre rev it up?
 

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Discussion Starter #20
So I am working on buying up parts in an attempt to solve this probelm. Can you clarify should I replace the front or back o2 sensor or both? and what do you recommend as a good replacement. CFM has both ford and bosch replacements any idea which is better? the bosch are cheaper but don't have quite as good of a review rating as the ford ones. If you know of a better place to buy em from let me know!
 
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