2002 XLT 4.0 SOHC Rough Idle

ccorder · August 21, 2008

Bought this truck last year. Has 85k on it. It idles at 600 rpm but has a roughness to it, warm or cold. I will replace the PCV and clean the IAC and MAF. However, I noticed the hose from the EVAP solenoid is dry rotted. It is not split and does not collapse but it does not fit on the solenoid very tight. Could this be causing the rough idle?

Thanks for any help on this item.

not8taxi · August 23, 2008

i got a 02 4.0 also...had the same rough idle problem but recently its been idling at around 500-600 rpms...never got around to it just work to much...let me know if you find out anything..i was lookin at the iac ...maybe a tuneup?...mine is overdue for sure...

aldive · August 23, 2008

Take a look at http://www.explorerforum.com/forums/showthread.php?t=169335&highlight=quest

rumpledoll · August 24, 2008

My 2002 V6 4.0L SOHC Eddie Bauer with 61,000 miles has a nice smooth idle. It was getting a very little bit rough but 6 new double platinum Champion spark plugs (first plug change), cleaned MAF, new PCV value, new fuel filter and new air filter has it purring away at idle.

I would trade a bit of that smoothness for better MPG though!

Before this Ex we had a 2000 4WD XLT with the SOHC 4.0L V6 and while that truck got better gas mileage than our current 2002, it had a very rough idle and other idling issues. Occasionally it would stall out at idle after oscillating high RPM to low at idle over an increasing range.

Rumple

rumpledoll · August 24, 2008

A vacuum leak can easily be the cause idle roughness. While replacing my PCV value a let the truck idle with the hose disconnected and the idle was very rough indeed.

To see if it is the evap line, remove the hose at the intake manifold side and temporarily plug the now empty hose with your finger or other object. If the idle improves you know its the evap system.

Rumple

ccorder said:
It is not split and does not collapse but it does not fit on the solenoid very tight. Could this be causing the rough idle?

trucku · November 12, 2008

There is a new flash for the computer that is supposed to address the rough idle among other issues like lean code errors.
I had it done today. Hope it cures my rough idle issue. I will see as the week progresses.
here is the new part number for it 1U7A 12A650

sethmorgan · November 13, 2008

trucku said:
There is a new flash for the computer that is supposed to address the rough idle among other issues like lean code errors.
I had it done today. Hope it cures my rough idle issue. I will see as the week progresses.
here is the new part number for it 1U7A 12A650

trucku, any news on the flash update?

sport97 · November 13, 2008

Im havin a rough idle on my 97 sohc. It seems like it misses randomly. Im gonna replace the PCV when i get time. I also have a leak somewhere. I cant find it. Its either a vacuum leak or a leak from the upper intake. It makes a fairly loud sucking sound and the throttle response is delayed too. Thats probably my issue more so that the PCV valve

trucku · November 13, 2008

sethmorgan said:
trucku, any news on the flash update?

Been driving her for couple of days now and she is running nice. I had a pretty shaky idle. You could feel when the truck was in park or drive and stopped. I honestly can say it feels better.
I am hoping the new flash will get me some better mileage..LOL
She feels better under foot.

I will update more in week or so during 2 more tank refills (to see if mileage has changed). I have been driving the same route everyday. I have all my mileage logged so far.

trucku · November 13, 2008

sport97 said:
Im havin a rough idle on my 97 sohc. It seems like it misses randomly. Im gonna replace the PCV when i get time. I also have a leak somewhere. I cant find it. Its either a vacuum leak or a leak from the upper intake. It makes a fairly loud sucking sound and the throttle response is delayed too. Thats probably my issue more so that the PCV valve

I changed the gaskets on my upper intake, new PCV, Ultrasonically cleaned my injectors and IAC. It made a difference in my opinion. My number 6 intake gasket had oil around and past it, so my intake was definitely leaking. I also installed a air dryer to catch all the oil that normally goes into the intake. Now when I remove my oil cap while engine is running you can hear the rpm change. before it never did that. I will put a vacuum gauge on one day to get a real reading.

sethmorgan · November 13, 2008

trucku said:
Been driving her for couple of days now and she is running nice. I had a pretty shaky idle. You could feel when the truck was in park or drive and stopped. I honestly can say it feels better.
I am hoping the new flash will get me some better mileage..LOL
She feels better under foot.

I will update more in a couple of days and during 2 more tank refills (to see if mileage has changed). I have been driving the same route everyday. I have all my mileage logged so far.

I have the same symptoms as you and have tried everything. I'm going to look into the PCM flash as well. Do you mind my asking how much the dealer charged?

trucku · November 13, 2008

sethmorgan said:
I have the same symptoms as you and have tried everything. I'm going to look into the PCM flash as well. Do you mind my asking how much the dealer charged?

I was in the service dept to get my cruise control and 4x4 issue fixed. The tech saw all my gadgets under the hood and began talking to me. He just did it for free as I was talking to him and didn't really say anything. To be honest I don't know if he did me a favor or I was not going to get charged anyways since I had other work done, so I don't know what it would cost. Sorry.

sethmorgan · November 13, 2008

trucku said:
I was in the service dept to get my cruise control and 4x4 issue fixed. The tech saw all my gadgets under the hood and began talking to me. He just did it for free as I was talking to him and didn't really say anything. To be honest I don't know if he did me a favor or I was not going to get charged anyways since I had other work done, so I don't know what it would cost. Sorry.

I just took a look under the hood to see what, if any updates had been done and i found a sticker with: 1U7A-12A650-B2A. So apparently I already have what you just got. And BTW, I get between 16 and 18mpg, so maybe this update will help you in that regard.

trucku · November 13, 2008

Wow thats great. Thanks for that information..

Oh wait..B2A... hmm ok I found what the tech wrote on a business card for me.
1U7A 12A650 GMB.... Its that still the same. I don't know much about the versions so this is confusing me.

I am sorry that I left that out... Honestly I thought he wrote his initials.

How newbie of me.

sethmorgan · November 13, 2008

trucku said:
1U7A 12A650 GMB.... Its that still the same. I don't know much about the versions so this is confusing me.

Interesting. I'm going to call the dealer and find out.

trucku · November 13, 2008

great. sorry for the confusion.

sethmorgan · November 14, 2008

trucku said:
great. sorry for the confusion.

No worries. I called the service dept at my dealer, and the manager transferred me to another manager's voice mail. weird. I'm going to hit them up again today and I'll report back.

sethmorgan · November 14, 2008

sethmorgan said:
No worries. I called the service dept at my dealer, and the manager transferred me to another manager's voice mail. weird. I'm going to hit them up again today and I'll report back.

So here's the deal: The 1U7A-12A650-GMB is the latest PCM upgrade for the 2002-2005 4.0L SOHC. It supersedes all previous ones, including my B2A. It solves a bunch of issues, one of which is idle and surge when no MIL or codes are present. The cost at my dealer is $98. The manager said it sounds like my truck would be a good candidate, but it's still a dice roll.

Trucku, my engine has a cyclic lope at idle. You can also see the engine shimmy to one side at the cyclic interval. Is this what yours did? And did it smooth out after the upgrade?

trucku · November 14, 2008

Great information!. Thank You for finding out.

The idle is definitely noticeably smoother by far. She is not totally a vibration less beast, but I think its time for a plug and wire change.

I my truck would idle very rough from day one of owning it. I could never get her to run smoothly. I am very pleased with the new flash.

I am not aware of the cyclic loop and how it would move over to one side. I just had very crappy and shaky idle. Come to think of it I do remember watching the engine kicking to one side more than another.

The driveablilty and over performance of the truck is better IMO. I will have mileage data on the next fillups.

I say go for it. Remember they cannot flash it backwards once you get the update.

Note: my intake gaskets and PCV was replaced. I cleaned my IAC and mass sensor in ultrasonic cleaner. All this done prior to flash.

sethmorgan · November 14, 2008

trucku said:
The idle is definitely noticeably smoother by far. She is not totally a vibration less beast, but I think its time for a plug and wire change.

I my truck would idle very rough from day one of owning it. I could never get her to run smoothly. I am very pleased with the new flash.

I just had it done and I can say ditto everything you just wrote. This is after driving it the 1 mile back from the dealership. I recommend anyone having the rough idle issue get this upgrade. Thanks for giving me the idea. Finally something I tried actually made a difference. I felt like I was tossing a $100 bill out the window every time I attempted another shot at fixing this.

2002 XLT 4.0 SOHC Rough Idle

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