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Discussion Starter · #1 ·
The day I went to the dealership I knew enough about the ST to know that I was going to buy one. Having come from a POS to the ST everything seemed perfect and smooth. I took the ST out for a test drive then signed the papers and went home with it. Happy, happy... right? Well, the next morning I started the car and as I sat in the car messing with the radio I felt a what I noticed a "bump" or "thud" from the idling engine. It's nothing audible, but I felt my whole body shift when the "misses" in the idling would occur. Over the last couple of weeks I've continued to feel the "bumps" when idling. Rarely it's bad enough that it feels like the engine is going to die when idling. I've taken it to the dealership. No codes.
I compared it to another ST they had just received and I feel the same thing VERY VERY slightly... so slight that I would not have had an issue with it, but in my car it's much more noticeable. The mechanics and their manager acknowledged the sensation when idling but, because no codes popped up, they had no idea why it was doing it.
The car runs fine otherwise (if you don't include the SYNC problems: system wouldn't turn on at all. Today, no volume control).
Anyone else noticed this rough, bumpy idling?
 

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Do the rough idle/bumps seem to happen more when the engine is cold, hot or all the time? If you try to hold the revs up slightly higher does the symptom still occur? It almost sounds like a slight or occasional vacuum leak somewhere.

I have not noticed that occurring in mine, but I haven't paid attention for that - I've only had my car for a week now. I will keep a closer eye on it when I head out at lunch today.
 

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I notice them, but the idle is much smoother than my previous car. Also, mine are very minor and not notable from a noise perspective. I hope they can sort this out for you.
 

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This was a severe problem with my Focus Titanium, but I get it every once in a while with my ST. No answer as to what's causing it. Dealer tech claims its a normal feature of direct injection (which I think is BS).
 

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Discussion Starter · #5 ·
Do the rough idle/bumps seem to happen more when the engine is cold, hot or all the time? If you try to hold the revs up slightly higher does the symptom still occur? It almost sounds like a slight or occasional vacuum leak somewhere.

I have not noticed that occurring in mine, but I haven't paid attention for that - I've only had my car for a week now. I will keep a closer eye on it when I head out at lunch today.
It happens whether the engine is cold or hot, happens any time I idle. Increasing the RPM, even very slightly, seems to remove the symptom.

The spacing between the symptoms is anywhere from .5 seconds to several seconds, meaning that it idles smoothly for .5 seconds to several seconds between symptoms. What concerns me most is the more noticeable symptoms that feel like the engine is going to die. The severe symptoms don't occur very often (maybe once or twice per day), but they shouldn't be happening at all in a brand new car. Keep in mind that it was doing this the night I got it home and I got it into the dealer asap. Also, I drive it very, very, very gently 99.9% of the time. It's extremely rare that I really romp on it, and I never hit the RPM limit, so it's not like I'm beating the crap out of it.
 

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I notice this too, but it is very, very, very faint.
 
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It happens whether the engine is cold or hot, happens any time I idle. Increasing the RPM, even very slightly, seems to remove the symptom.

The spacing between the symptoms is anywhere from .5 seconds to several seconds, meaning that it idles smoothly for .5 seconds to several seconds between symptoms. What concerns me most is the more noticeable symptoms that feel like the engine is going to die. The severe symptoms don't occur very often (maybe once or twice per day), but they shouldn't be happening at all in a brand new car. Keep in mind that it was doing this the night I got it home and I got it into the dealer asap. Also, I drive it very, very, very gently 99.9% of the time. It's extremely rare that I really romp on it, and I never hit the RPM limit, so it's not like I'm beating the crap out of it.
This is EXACTLY my experience with my car. I've stalled a couple time reversing out of my parking spot because of the rough idle. It's ridiculous. But it sounds like this is a known, but not yet resolved, problem. I've looked for bad connections, exposed wires, etc., but I can seem to find any. I've had this problem since day one, both before and after installing an aftermarket ECU tune.
 

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How often is it repeating? Is the car doing it for long period of time and then the symptoms go away, does it happen for a few times in a row then stop, or is it continually doing it to varying degrees?

Just what has been described it could be a few different things but if I had to guess what's most likely I'd say bad MAP (manifold absolute pressure) sensor that has a dead spot in its output, possibly a crank or cam sensor issue, a wiring issue with the pressure solenoid on the high-pressure mechanical direct injection pump or a vacuum line leak or evap component issue. A scan tool with high-speed sampling and access to Ford's enhanced OBD-II data would be handy but if it is electrical and only occurs for a fraction of a second a scope might be required to probe different circuits as some events might be of too short a duration to see over OBD-II and might not be enough to trigger a code in the computer.

Another thought is an issue with the A/C compressor clutch cutting in and out. If you have the system turned on, in the auto setting or using defrost or blend-defrost modes the car should be cycling the compressor. I've seen some issue where improperly charged A/C circuits, bad compressor clutches, or constantly cycling compressor clutches due to other electrical issues will cause an increased load or sensation. An easy way to rule out a clutch issue would be to pull the fuse for the A/C system.

Last and something that would probably be more widespread is if there's an issue with the engine calibration (tune). Depending on how the aftermarket tuning devices are working with the Bosch controller, if the tuning device is only rewriting certain tables, or even if they're rewriting the entire calibration, they likely haven't altered the base code (some people call this the operating system but a better term would be a real-time program/integral operating system) so it could be possible to have something in the calibration that persists even with a tune.
 

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Eric, as far as what I'M experiencing, it only happens at idle, and i will feel a very, very faint bump like every, I would say, 3-8 secs. Nothing seems to be effected by this, so I don't really think it is an issue. I have noticed this with a number of cars I have had in the past, both tuned, and untuned.
 

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I haven't noticed it in my ST, but my direct injection, turbocharged Cobalt SS will on very rare occasions have a slightly stumble or miss you can feel immediately after start-up if you drive off right after starting the car when the engine was cold. It also seems to be worse on cooler days. On turbocharged vehicles where that only use a single catalyst (like the ST) and having a turbocharger in the exhaust stream before the cat the engine controller has to run the engine fairly rich on cold starts to help aid catalyst heat up. I suspect what I was seeing in the Cobalt was the engine still in cold-start mode and not switching out of that mode fast enough.

An easy way to rule this out if anyone is having an issue at idle immediately after startup is to start the car, don't press the gas pedal (which often drops out of cold-start on many of the newer Bosch controllers) and let it run for a minute or so before driving off. If you still feel something after the car has warmed up to operating temperatures it's likely something else.
 

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Blackbird - thanks very much for your thoughts on this. As the OP posted, the "stumble" or "shake" occurs both when the car is cold, and when it has been driven for a long time, but only occurs at idle. The problem does seem slightly worse when the car is cold, but never entirely goes away. I wonder if playing with the idle speed would help matters. I'm sure Torrie could adjust that pretty easily with his tune.
 

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If it's happening like you describe when warm or cold and doesn't go away I'm not sure changing idle speed is the best solution. It might be a band-aid but it would be nice to track down the root cause. I'd probably start with a really good physical inspection of all the vacuum line from the front of the car to the rear evap lines at the gas tank, then look at the underhood electrical connectors and wiring harness, especially at the sensor, throttle body, etc.

If it still persists and bothers you then you could try throwing parts at it or keep taking it to the dealer but unless someone does some logging and electrical diagnostics to rule items out it might be tough to find. Drivability concerns can sometimes be like trying to track down NVH (noise, vibration, harshness) problems. You almost hope they're big problems as it makes it easier to find the source and either way a good tech well versed in that area can be invaluable.

You did mention having a tune and if that's using an SCT handheld flasher, if they're supporting the ST for enhanced data logging you could also try to log a couple of the sensors at a time such as the MAP, throttle position, O2 sensor, crank timing, etc. to see if there are any spike or anomalies. Usually logging just a couple sensors/reading will get you a faster sampling rate over the bus but if it turned out to be electrical an oscilloscope might be needed. Hopefully it's something minor and Ford can find a solution to those having a problem.
 
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All the 4 bangers I've had seem to do this, some more than others. My ST does it, but not as bad as the Saab does. I wouldn't sweat it unless its just too bad of a stumble.
 

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Discussion Starter · #15 · (Edited)
Thanks for all the feedback. It's still happening but much less noticeable now.
Now I'm dealing with the latest software update! :D

The update started and seemed to be going as planned, but as the 4th file was being updated it went it to an infinite crash/shutdown/reboot loop. I removed the USB drive and it's been trying to "fix itself" for several days now. Have any of you tried to update to the latest software? If so, did it work? If not, have you found a work-around?

Also, got the first chip in the paint (errant rock on freeway) on the hood. Where can I get touch-up paint? Is that the way to go? Other options?
 

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Mine does this as well. Figured it's normal in a performance 4 cylinder engine with a turbo. I came from a Neon SRT-4, so it's quite tame by comparison. It never hesitates or stumbles when I give it gas, so doesn't bug or worry me.
 

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I have noticed mine getting worse. In fact the day before yesterday it did something really weird, it almost died after I started it, then would boost to 1500 RPM, then go down to 500RPM and catch itself from stalling and boost back to 1500 rpm all while sitting in neutral on a 70 degree day after just starting it. I drove it for about 5 minutes, pulled over and put it in neutral and it continued with the same symptoms. I turned it off and back on and it fixed itself, but the noticeable rough idle that most of you are speaking about here seemed worse. I recorded what it was doing to show to the dealer when I take it in this week.
 

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This was a severe problem with my Focus Titanium, but I get it every once in a while with my ST. No answer as to what's causing it. Dealer tech claims its a normal feature of direct injection (which I think is BS).
Yes, that is indeed bullshit.

FYI my car has a rough idle for the first 30 to 50 miles after flashing a new tune (which is normal). Just throwing that out there.
 

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My car idles rough when heat is on and I didn’t know if it’s caused by a vacuum issue if anyone could help I would appreciate it.
 
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