3.8 rough idle and dead spot

BumblebeeZA

BumblebeeZA

New member
Hi all,

I did some searching on the forum but couldn't quite find all the info I was looking for.

I have an 08 JKUR (right hand drive as Im in South Africa) with 110 000km's (68 000 miles) I noticed about 3 months ago that after about 5 mins of driving my Jeep would start to shake for a few seconds then idle normally for the rest of the time thereafter.
Then about 1 month ago, my Jeep started doing this strange thing in the cold mornings, where I would start it and drive but the first 1 min of driving it would be like a dead spot, I would press the throttle down but almost nothing happens then all of a sudden a surge of power.... after a like 1 min it would go on as normal.

This morning however, I started my Jeep and it was shaking shaking shaking but at steady revs, after 5 secs it was idling smoothly again.
My Jeep was serviced 5000km's ago, and also until resonantly it has started burning oil but that is not of much concern to me as it seems quite normal and its only like 500ml every 3000km's - 5000km's.

Current morning temps are averaging around 10C (50F).
I have read about IAC, TPS and PCV that could be causing my symptoms, please advise :)
 
cozdude

cozdude

Guy with a Red 2-Door
BumblebeeZA said:
Hi all,

I did some searching on the forum but couldn't quite find all the info I was looking for.

I have an 08 JKUR (right hand drive as Im in South Africa) with 110 000km's (68 000 miles) I noticed about 3 months ago that after about 5 mins of driving my Jeep would start to shake for a few seconds then idle normally for the rest of the time thereafter.
Then about 1 month ago, my Jeep started doing this strange thing in the cold mornings, where I would start it and drive but the first 1 min of driving it would be like a dead spot, I would press the throttle down but almost nothing happens then all of a sudden a surge of power.... after a like 1 min it would go on as normal.

This morning however, I started my Jeep and it was shaking shaking shaking but at steady revs, after 5 secs it was idling smoothly again.
My Jeep was serviced 5000km's ago, and also until resonantly it has started burning oil but that is not of much concern to me as it seems quite normal and its only like 500ml every 3000km's - 5000km's.

Current morning temps are averaging around 10C (50F).
I have read about IAC, TPS and PCV that could be causing my symptoms, please advise :)
Click to expand...

Sounds like the motor isn’t getting enough air. I would start with simple checks like checking your air filter. After that check your throttle body and clean all the excess carbon off of it and around the throttle plate. The build up of carbon in this area can lead to harder starts due to it restricting air flow.
 
BumblebeeZA

BumblebeeZA

New member
madstiles said:
When it was serviced did they replace the spark plugs and wires?

Sent from my SAMSUNG-SM-G935A using WAYALIFE mobile app
Click to expand...

Yip, plugs and wires.... and I think that was on the 96000km service if I recall correctly... I remember that was a BIG one, all my oils etc were done too.
I do remember seeing my throttle body looked a little dirty as mentioned above I should clean that.

Ill try some carb cleaner and a rag this week and clean as much as possible while its still fitted to my Jeep.
Just to recap, this only happens when cold, like lunch time now I went out and iall is fine, but its like 20C outside so its not cold really.


Thanks for the replies so far guys!
 
jknikos

jknikos

Member
Check your manifolds fro cracks. It is very common on our motors. A cracked manifold will affect cold start behavior and when it gets hot the crack minimizes so it drives normal.
 
BumblebeeZA

BumblebeeZA

New member
cozdude said:
Sounds like the motor isn’t getting enough air. I would start with simple checks like checking your air filter. After that check your throttle body and clean all the excess carbon off of it and around the throttle plate. The build up of carbon in this area can lead to harder starts due to it restricting air flow.
Click to expand...

I have a KnN flat filter in the air box and its been resonantly cleaned and reoiled.
I did notice my throttle body looked a bit black the last time I checked. Can I use some carb cleaner and a rag? while still fitted to the Jeep or must I remove it completely?
 
BumblebeeZA

BumblebeeZA

New member
jknikos said:
Check your manifolds fro cracks. It is very common on our motors. A cracked manifold will affect cold start behavior and when it gets hot the crack minimizes so it drives normal.
Click to expand...

Yeah thats was a worry of mine, but had them checked on the last service too as I noticed a "air blowing sound on cold startup and they were fine, HOWEVER the exhaust was loose on the manifold so they tightened that up and the sound was almost gone but it seems to becoming back again, maybe they are loose again and need a tighten, Ill check that out too this week thanks bro!
 
jeeeep

jeeeep

Hooked
BumblebeeZA said:
I have a KnN flat filter in the air box and its been resonantly cleaned and reoiled.
I did notice my throttle body looked a bit black the last time I checked. Can I use some carb cleaner and a rag? while still fitted to the Jeep or must I remove it completely?
Click to expand...

It's easier to clean the TB with it off, you don't want all that crap to flow into the engine.

don't overtighten when you put it back on, the plastic housing cracks easily.

if the TB butterfly is sticking, it will do as you describe until it's warmed up.

PCV valve are cheap and easy to change.
 
BumblebeeZA

BumblebeeZA

New member
jeeeep said:
It's easier to clean the TB with it off, you don't want all that crap to flow into the engine.

don't overtighten when you put it back on, the plastic housing cracks easily.

if the TB butterfly is sticking, it will do as you describe until it's warmed up.

PCV valve are cheap and easy to change.
Click to expand...


Great thanks! I think I have a job on my hands this week end then with my TB and Carb Cleaner ;)
 
K

Kavanji

Member
BumblebeeZA said:
I have a KnN flat filter in the air box and its been resonantly cleaned and reoiled.
I did notice my throttle body looked a bit black the last time I checked. Can I use some carb cleaner and a rag? while still fitted to the Jeep or must I remove it completely?
Click to expand...

there is your problem. the oil of the k&n gets sucked into the intake and some of it sticks to the sensors in the intake system. clean everything with carb cleaner and NO rag. dont wipe the sensors down, just flush them with carb cleaner.
that should do the trick.
 
BumblebeeZA

BumblebeeZA

New member
Kavanji said:
there is your problem. the oil of the k&n gets sucked into the intake and some of it sticks to the sensors in the intake system. clean everything with carb cleaner and NO rag. dont wipe the sensors down, just flush them with carb cleaner.
that should do the trick.
Click to expand...

Great! Would I need to be replacing any gaskets when doing this?
I am quite hands on with basic mechanical work but I dont wanna take apart my intake system and then need gaskets when putting it back together so Id rather get whats needed first before I start
 
BumblebeeZA

BumblebeeZA

New member
UPDATE:

So last night I decided to not wait for the week end and clean my Throttle Body immediately.
I took it off, and OMG it was FILTHY!
Sprayed the living crap out of it and it is clean clean clean again, one issue I have is that the oring "Gasket" was melted at the bottom half, it still has some seal capabilities, so I put it back together for now and will order a new seal.

This morning, Jeep started up perfectly and idled fantastic.
I also bought some injector cleaner that Ill be throwing into my tank on the next fill up then I know thats done too.

Thanks for the advice guys, much appreciated ;)
 
cozdude

cozdude

Guy with a Red 2-Door
BumblebeeZA said:
UPDATE:

So last night I decided to not wait for the week end and clean my Throttle Body immediately.
I took it off, and OMG it was FILTHY!
Sprayed the living crap out of it and it is clean clean clean again, one issue I have is that the oring "Gasket" was melted at the bottom half, it still has some seal capabilities, so I put it back together for now and will order a new seal.

This morning, Jeep started up perfectly and idled fantastic.
I also bought some injector cleaner that Ill be throwing into my tank on the next fill up then I know thats done too.

Thanks for the advice guys, much appreciated ;)
Click to expand...

Glad that worked out for you!
 
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