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  #1  
Old 04-13-2011, 11:18 AM
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Very Rough Idle when Cold

Hi guys,

I've done some searching and have seen mixed results, so I thought I'd start my own thread.

This is for my í07 FX4 5.4L. Only modifications are Gryphon tuner, exhaust, and CAI. Iíve already ruled out the programmer as a possible cause by returning it to stock for an entire tank of gas.



Had my 60K tune-up done a few weeks ago. This included the regular stuff along with an early plug change. It went very well and none broke, thankfully.

Well, about two weeks after the tune-up I noticed the truck idling rough during cold start-up. To go along with that, it had some hesitation when pulling from a dead stop. For example, if I started the truck and pulled out to my neighborhood stop sign, the engine hesitates when pulling away from the stop sign. The RPMs bounce around like crazy.

They also bounce around during cold idle, and I can feel the engine vibrating (jerking is the best way to describe it). I can rev it to between 1200 and 1400 RPMs and it gets really badÖ..the truck starts shuddering. Feels like it might die but doesnít.

This all happens when the engine is cold. Once it starts to warm up itís fine---no hesitation and no bouncing RPMs.


Well, it hasnít been that bad so Iíve been trying to wait until a good time to take it to the mechanic in order to avoid having to get a rental car. We have two days off work next Thursday and Friday, so Iím trying to make it to then. Iíve just been letting the truck warm up for 10-15 minutes in the morning before pulling out.



Flash forward a few weeks to this morning. The past few days I havenít been warming the truck up like usual. The hesitation seemed to be gone but the RPMs still bounce around at idle. Iíll pull up to a red light and they bounce between 600 and 900 RPMs constantlyÖ.slightly shaking the truck. Nothing major but it isnít very comforting having the feeling that something is wrong.

This morning it was really bad---the worst itís been so far. The rough idle was really rough, the hesitation was back, and worst of all it did it for about 10 minutes even after the truck warmed up. Driving down the road the truck was shaking terribly due to the engine running so rough. It was vibrating so bad I was scared that I wouldnít be able to make it to work. Once I got on the interstate it was fineÖ.


Mechanic is out due to medical emergency for a few days, so Iím going to try to get it in next week. From my research and talking to my mechanic (about two weeks ago), we seem to think itís one or more of the coils going bad.


Any other ideas? From my research around the boards it could be a few things (vacuum leak, coils, etc). What do you guys think? This has me worried because of how bad it was this morning.

Thanks for any help!

-Matt
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  #2  
Old 04-13-2011, 11:22 AM
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could be dirty MAF and throttle body, dirty fuel filter, bad spark plug, failing COP. Could also be a vacuum leak.
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Old 04-13-2011, 01:33 PM
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Quote:
Originally Posted by Bluejay View Post
could be dirty MAF and throttle body, dirty fuel filter, bad spark plug, failing COP. Could also be a vacuum leak.
Thanks Bluejay. I replaced the fuel filter a few months ago, so it should be fine. I think he cleaned the MAF and throttle body during the 60K tune-up, but I'll have to double check with him.

Spark plug might be a good possibility since they were replaced a week before it started doing this.

One thing that does stand out that you mentioned is the vacuum leak. I did notice that this little guy (circled in white) is loose. It goes on tight enough not to come off, but it doesn't snap into place like it should. I assumed since it was on tight enough not to come off that it wouldn't be the cause.


Click the image to open in full size.





I'm just hoping that this isn't one of those scenarios where he ends up replacing 10 things on the truck trying to fix this problem....
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Old 04-13-2011, 01:37 PM
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If you have a tuner or scanner, try reading codes. It can register problem codes without ever doing a CEL.
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Old 04-13-2011, 01:40 PM
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I do on a regular basis....unfortunately nothing new has popped up. I get CELs every few weeks (p0420/30) since I have hi-flow cats, so I check and clear them every so often. Unless it's a possible exhaust leak....but I don't see how that would cause this since it's already past the engine.
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Old 04-13-2011, 01:48 PM
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No, would not be the exhaust unless it's O2 sensor related.
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Old 04-13-2011, 01:48 PM
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I'm betting a plug.
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Old 04-13-2011, 02:31 PM
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Quote:
Originally Posted by Bluejay View Post
No, would not be the exhaust unless it's O2 sensor related.
This is also listed here as a possible cause?
http://www.obd-codes.com/p0420
Quote:
An oxygen sensor is not reading (functioning) properly

I'm probably going to ask him to check the plugs first since they were changed a week before this started.
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Old 04-13-2011, 03:09 PM
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Quote:
Originally Posted by mblouir View Post
Thanks Bluejay. I replaced the fuel filter a few months ago, so it should be fine. I think he cleaned the MAF and throttle body during the 60K tune-up, but I'll have to double check with him.

Spark plug might be a good possibility since they were replaced a week before it started doing this.

One thing that does stand out that you mentioned is the vacuum leak. I did notice that this little guy (circled in white) is loose. It goes on tight enough not to come off, but it doesn't snap into place like it should. I assumed since it was on tight enough not to come off that it wouldn't be the cause.


Click the image to open in full size.





I'm just hoping that this isn't one of those scenarios where he ends up replacing 10 things on the truck trying to fix this problem....
I (Had) an AFI intake on mine for awhile, that connection felt loose on mine also, so I don't think that would be a concern with yours. Curious what you find out though, Good Luck
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Old 04-13-2011, 03:23 PM
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After having my plugs done and TB cleaned, a few days later I had the RPMs drop and felt like it almost died. It also has ran rough at idle once since the plug change. Hope you get it figured out I would like to know for future reference as well.
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  #11  
Old 04-14-2011, 08:02 PM
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Noticed some new symptoms today:


When driving the truck seems to idle higher than it should when my foot is off the pedal. Difficult to describe but almost like it's pulling itself. Think of a stick shift...you can stick it in first and it will creep along without you having to hit the gas. Not exactly that but similar. I was coasting today around 50,55mph and when I let off the gas it didn't slow down like it used to....almost like it was trying to fight from slowing down.

Another thing that I would assume goes along with the previous....
On the Gryphon you can show instant mpg (IMPG). Normally if you're above 35, 40mph and you let your foot off the gas to coast the IMPG go to 40+. Mine has always shown that. Today, though, I noticed that it never hit above 30 IMPG. It's almost like the throttle is higher than where it should be.


Any ideas?
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Old 04-14-2011, 08:49 PM
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Just thinking out loud here...

Plug or bad coil is one of my first thoughts... I'll tell you, when I had a misfire how crap my truck shook


This could be just a shot in the dark, but when you say the truck seems to keep going, what about a TB sticking opened? Like the butterfly not opening and closing as well as it should?
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Old 04-18-2011, 09:48 PM
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updates Matt?
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  #14  
Old 04-18-2011, 10:12 PM
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Man you've got great timing. I dropped the truck off earlier this afternoon. Should have it back within a day or two. Will let you know what it turned out to be.
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Old 04-19-2011, 11:02 AM
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Just looking out for a bud

I'll be waiting
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Old 04-19-2011, 11:02 AM


 
 
 
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