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1999 Chevy Lumina 1999 Lumina Sedan rough idle when cold go

Tiny
HSOBCHINSKY
  • MEMBER
  • 1999 CHEVROLET LUMINA
Engine Performance problem
1999 Chevy Lumina 6 cyl

It all happened one day when I started the engine in the morning and noticed a very rough idle but soon went away when it warmed up. Then I got a fault code misfire cyl. #1. I tried new plugs, wires, no good. I had the injectors cleaned proffesionally, no good. I replaced cyl. #1 fuel injector and seemed to run great for the first day, 2nd day started all over again and getting worse. I did a compression check on all 6 cylinders and they all held @ 160 for at least 20 minutes each. I did notice that I am "very slowly" loosing coolant but do not know from where and sometimes you can smell the burning coolant when engine is hot.
Any suggestion's as what to look for next?
Extreamly frustrated!
Thank's
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Tuesday, May 19th, 2009 AT 9:58 PM

6 Replies

Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Check and suspect intake manifold gasket
check for leaks under the throttle body area top of tranny
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Wednesday, May 20th, 2009 AT 5:55 AM
Tiny
HSOBCHINSKY
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Intake gaskets where replaced when plenium was removed to access all fuel injectors. But I checked anyway and no leaks. I also checked for leaks around throttle body, cant find any.
Just a note, the rough idleing not only happens when engine is cold but now it happens when ever I start the car. Then after about 1 minute and reving the gas peddle a few times the rough idle goes away.
Any suggestions?
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Wednesday, May 20th, 2009 AT 12:27 PM
Tiny
BMRFIXIT
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Lower intake gasket !!
I would suspect an injector issue
try and due an injector leak test and balance test

*****************************************
need manual CHECK IT @
https://www.2carpros.com/kpages/auto_repair_manuals.htm
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Wednesday, May 20th, 2009 AT 10:01 PM
Tiny
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  • 5 POSTS
What do you mean by lower intake gasket?
I already replaced the injector with a "new" one.
How do you perform an injector leak or balance test?
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Thursday, May 21st, 2009 AT 1:20 AM
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Coolant leak !!
very common for the lower intake manifold gasket to be leaking
you take the upper to get to the injectors
injectors site on top the lower intake manifold
balance test can be done using a scanner
leak test need fuel pressure gauge
check fuel pressure after engine of if pressure drop quickly or not

*****************************************
need manual CHECK IT @
https://www.2carpros.com/kpages/auto_repair_manuals.htm


https://www.2carpros.com/forum/automotive_pictures/99387_Graphic1_356.jpg

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Thursday, May 21st, 2009 AT 5:42 AM
Tiny
HSOBCHINSKY
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Well I finally took your suggestion and tore down the engine. What I found was lower intake gasket split and leaking just above the trans bell housing and decided to pull the rear cylinder head off also. What I found there was I think cylinder #2 definately is burning coolant, this cyl. Is extreamly clean and wet compared to the other two that have carbon build up.

I could not find where the coolant is entering from, I inspected the Head, Gasket and Cylinder walls. The only suppision I have is a vertical white line on the cylinder wall and I sent a pic.

What I don't understand is before the tear down I did a pressure test on all cylinders and they all held pressure about (100 psi) for about 2o minutes each. How can I find where the coolant is coming from.
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Tuesday, July 21st, 2009 AT 8:20 PM

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