3.8 idle problems

jknikos

Member
Hello fellow jeepers! Last week suddenly my 3.8 jk sport started to have unstable idle when the engine was in operational temp. The problem got worse as when i was for a period of time in traffic. Also my idle is low at 600rpm. When the engine is in gear it works as it used to. The problem is when idle. I tried to put gas from a different gas station and the problem is still there. Then i changed spark plugs and spark wires. My spark plugs had a very big gap and they were worn out, my spark wires seemed ok but i changed the just in case. My engine runs better now but the idle problem is still there. My engine has 100000miles and i have no DTCs!!! Any thoughts?:thinking:
 
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jeeeep

Hooked
you can try to reset the ECU, if it doesn't work you will likely need to replace the coil pak - the following instructions are from Quadratec:

http://www.quadratec.com/jeep_knowledgebase/article-89.htm


1. Disconnect the battery by removing the positive battery cable. Remember, the positive battery cable.

2. Ground the positive cable to the negative cable for 30 seconds to erase the electric charge in the capacitors.

3. Reconnect the positive cable to the battery.

4. Turn the key to on but do not start.

5. Turn the headlights on.

6. Turn the headlights off.

7. Turn the key off.


The ECU has now been reset to its factory settings. For the next 50 warm-up periods the ECU will re-learn the engine and driving habits for your driving conditions and the newly installed parts.
 

jknikos

Member
I forgot to say that i run a superchips tuner. When the problem started i had 91performance programm. Then i changed to stock and then to 87. Problem appears in every programme. Does this reprogramming count as the ecu reset or not?
 
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ScoobyCarolanNC

Caught the Bug
Just went through this myself this summer. 2010 3.8 80K miles.

Plugs were gapped correctly? I bought Champions that were pre gapped, but one was off. Keep in mind +\-.02 is the margin of error.

Torqued to 12lbs (I think that was the spec)?

Wires are clicked into place? One of mine seemed so, but wasn't. My wires were pre greased but if you had to take them off & on as many times as I did, may not be a bad idea.

Throw away & replace your PCV valve. It's behind the coil. They get sticky & can cause vacuum issues.

Get 2 bottles of Lucas Oil Fuel Treatment & run them through a tank of gas each. I thought it'd be snake oil but it helped my rough idle noticeably.

My jeeps not perfect, but it's a hell of a lot better now. Hope this helps!
 

jeeeep

Hooked
I forgot to say that i run a superchips tuner. When the problem started i had 91performance programm. Then i changed to stock and then to 87. Problem appears in every programme. Does this reprogramming count as the ecu reset or not?

superchips tune is separate and does not reset the ECU.

However, I have experienced my Superchips tuner not install a program properly after making changes from one tune to another. What I had to do was return it to the stock tune, start the Jeep, no driving just start it, shut it off and then install the tune again.

Your ECU is pretty much constantly changing to learn your driving habits and seeing that your plugs were so worn out it probably still has the adjustments in memory that it made trying to adjust for your bad plugs/wires
 

jknikos

Member
Just went through this myself this summer. 2010 3.8 80K miles.

Plugs were gapped correctly? I bought Champions that were pre gapped, but one was off. Keep in mind +\-.02 is the margin of error.

Torqued to 12lbs (I think that was the spec)?

Wires are clicked into place? One of mine seemed so, but wasn't. My wires were pre greased but if you had to take them off & on as many times as I did, may not be a bad idea.

Throw away & replace your PCV valve. It's behind the coil. They get sticky & can cause vacuum issues.

Get 2 bottles of Lucas Oil Fuel Treatment & run them through a tank of gas each. I thought it'd be snake oil but it helped my rough idle noticeably.

My jeeps not perfect, but it's a hell of a lot better now. Hope this helps!
I used champion pregapped. I checked spark plugs and wires and everything is fine and brand new. PCV replaced last month.

When you say fuel treatment you mean the kind of stuff to clean the injectors? Cause this is something i am planning to use. I cannot find lucas oil brand here so i will go with some other reputable brand.
 

jknikos

Member
superchips tune is separate and does not reset the ECU.

However, I have experienced my Superchips tuner not install a program properly after making changes from one tune to another. What I had to do was return it to the stock tune, start the Jeep, no driving just start it, shut it off and then install the tune again.

Your ECU is pretty much constantly changing to learn your driving habits and seeing that your plugs were so worn out it probably still has the adjustments in memory that it made trying to adjust for your bad plugs/wires
Ok first i will do the procedure you describe with superchips then if problem is still there i will reset the ECU. :fingerscrossed:
 

BlackHawk08jk

New member
Try running a tank of super unleaded through it and see if it stops mine did that and I ran a couple tanks of super and it quit
 

jeeeep

Hooked
I used champion pregapped. I checked spark plugs and wires and everything is fine and brand new. PCV replaced last month.

When you say fuel treatment you mean the kind of stuff to clean the injectors? Cause this is something i am planning to use. I cannot find lucas oil brand here so i will go with some other reputable brand.

did you double check each gap before installing them? I always find the gaps to be off a little on some.
 

ScoobyCarolanNC

Caught the Bug
I used champion pregapped. I checked spark plugs and wires and everything is fine and brand new. PCV replaced last month.

When you say fuel treatment you mean the kind of stuff to clean the injectors? Cause this is something i am planning to use. I cannot find lucas oil brand here so i will go with some other reputable brand.

Yeah, you dump a bottle into your empty tank & then fill up on 91/93 octane. I had Lucas Oil brand so I can only recommend that, but you get the gist.
 

JeepFan

Active Member
I honestly don't think a bottle of petroleum distillate is going to solve this problem.

I recommend you take it to a shop that has a diagnostic scan tool.

If the engine is mechanically good, and the gas and injectors are good, there are lots of emission control devices that can cause a rough idle.

It's not uncommon for a bad oxygen sensor to cause a idling problem and not trigger the CEL.

If you are running an engine tuner, make sure you reset your JK back to stock before taking to a shop.

Just my 2 cents.
 

jknikos

Member
I reinstelled the superchips programm and i drove the jeep 3-4 timew this weekend. Seems like the problem is solved. I didnt even reset the ecu. It seems like the ecu had some adjustments for my extremely bad spark plugs wich did not change imediatelly after replacing them. After 4 trips now my ecu have been adjusted to my new plugs. Hope that my problem is solved :D
 

monstrousmac

Caught the Bug
Idle problems

I had a similar problem with one of my other jeeps same problem. I changed the idle position sensor and the throttle position sensor it was like new. just Google Jeep JK idle position sensor and jeep wrangler jk throttle position sensor.
 

jknikos

Member
I had a similar problem with one of my other jeeps same problem. I changed the idle position sensor and the throttle position sensor it was like new. just Google Jeep JK idle position sensor and jeep wrangler jk throttle position sensor.
I will check that, too :thumb:
 

jeeeep

Hooked
when you install new parts that affect the performance, resetting the ECU makes the learning process of the new parts faster.
 
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