vibrations / rough idle

[diyman]

Hi guys, small issue which is pi..ing me off!
I know my kj is no longer 'fresh', but has only 47 kmiles and I've always been caring her ( as everyone knows).

Apparently, she has started developing sort of 'rough idle', something like when radiator fans are full of mud..
I've cleaned the throttle body twice, but hasn't gone much better. Oil is fresh, filter too, tensioner is just 10k old and belt is new.
Also, checked for air leaks, spark plugs look OK, battery is new (they last 12 to 18 months here )

I'm considering engine or transmission mounts, or maybe water pump or related parts... Muffler is aftermarket and yes, maybe....

Any clue? don't feel like starting to change parts at random....

 

[LibertyTC]

Have you had any check engine lights or codes?
Fresh spark plugs every 25k miles, if they have not been done, as well as a good throttle body cleaning, including the IAC and TPS and ports.
The IAC (air intake control can get quite carboned up, and some throttle body spray cleaner and Q-tips applied on the IAC may do the trick.
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The IAC requires Torx bit to remove.

 

[diyman]

Thanks LibertyTC, I will try that ASAP!

No, No codes. I'm always checking that, even if MIL is off. In fact, many DTCs don't illuminate the MIL and are accessible by a (good) scanner only, I know.

Spark plugs are NGKs made in France, only 18k on them, but I'll try cleaning first. Coils going South???

 

[LibertyTC]

Coils will throw a misfire code.
I still would do fresh plugs now and check the gaps....to eliminate that as potential problem.
The IAC controls idle..so clean that sucker and ports!
PS if the spring is real super easy to press down on the IAC plunger, you might have to replace the IAC. There should be some reasonable resistance.

 

[diyman]

Tnx LibertyTC. I'll keep You informed

 

[New Liberty]

Sounds like a plug gone bad.

 

[Warren.fischbeck]

Does the roughness disappear when the engine warms up? When was the last time you ran some seafoam through the ol girl?

 

[diyman]

Does the roughness disappear when the engine warms up? When was the last time you ran some seafoam through the ol girl?

Yes, it does get a bit better. Seafoam, here, in Peoples's Republic of Venezuela?? :happy175:

Only can get some sort of sprayable carburetor cleaner many apply throught the intake duct....

About the one plug gone bad, yes, maybe, but shouldn't that also set a misfire DTC?

 

[Warren.fischbeck]

If you have a non-optimal spark it shouldn't set off the CEL, the computers have a range of aceptable parameters... New, properly gapped plugs could make the biggest impact.

 

[TAHOE]

Yep, do the easy stuff first, plugs & cleaning. Come to think of it, my wife's
'05 has 60K and original plugs, need to do hers too.

I was talking to my brother in law last night about the 3.7L & 4.7L developing misses ( dropped of my neighbors 03 dodge pickup w/3.7L, bad miss for him to work on) He said the aluminum heads have steel valve seats and sometimes due to different metal expansion rates, the steel seat will slightly come out, then **** sideways causing poor seating valve and miss. That will set off SEL light though. Not saying that is your problem, just something I recently learned.

 

[diyman]

I'm back. Task executed!

Report:

Spark plugs ( not OE set ) surely had better days - replaced

IAC (never unmounted before) was a read 'sludged coalmine' - cleaned
Re-applied a tiny bit of soft thread locker onto the T-20 torx screw.

Outcome:

Engine starts with NO hesitation. Some residual vibrations, but more 'regular'.

But, wait, I guess I've found a leaking hose! Shall get a new one ASAP. It's
the one which connect throttle body to PCV/breather.

Thanks a lot to Everyone in this thread grouphug.gif

 

[LibertyTC]

Glad you got the "Coal" out of the mine shaft.
Just use some electrical tape on the old PCV hose until new one arrives.
That should get you better running and fuel mileage.
Note the KJ coils spark the plugs pretty hot, change them ever 20K and it will respond better. Keep a Clean air filter in the KJ too.
Clean the IAC once a year as well.
Happy trails!:icon_lol: