99" Sts, Rough Idle When Cold. Help!!!
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Northstar Engines and System Technical Discussion Discussion, 99" Sts, Rough Idle When Cold. Help!!! in Cadillac Engine Technical Discussion; Hi guys, I have a 99 sts with 80k miles. The engine shakes terribly on cold start ups until it ...
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    VIPERRACING is offline Cadillac Owners Member
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    99" Sts, Rough Idle When Cold. Help!!!

    Hi guys, I have a 99 sts with 80k miles. The engine shakes terribly on cold start ups until it warms up. It looks as if it has a broken motor mount from how bad it shakes. I have no clue whats wrong with it. Can someone show me a pic of the were the egr valve is so that I can make a block off plate for it. Thanks for any and all help.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: 99" Sts, Rough Idle When Cold. Help!!!

    Block off the EGR and you wind up with incredible ignition knock. Better to fix the real problem.

    Any trouble codes come up ? If the engine shakes until it warms up, then there's a problem with some emission contol function which drops off when the system goes closed loop.

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    VIPERRACING is offline Cadillac Owners Member
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    Re: 99" Sts, Rough Idle When Cold. Help!!!

    No codes. Will I still get knock if I keep it plugged in so that the computer still reads it after I block off the egr? thanks for all your help.

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    Highline Cady's Avatar
    Highline Cady is offline Cadillac Owners Fanatic
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    Re: 99" Sts, Rough Idle When Cold. Help!!!

    Could be pistons, generally referred to as "piston slap." That kind of can come and go. Sounds like a ford diesel at times. As I think about it however I think that problem was more common on 02-03's. Cams were known to give a lousy idle, the fix=replacement cams.

    Hope it's nothing that serious, good luck.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 99" Sts, Rough Idle When Cold. Help!!!

    Piston slap aka cold carbon rap is noisy, but doesn't cause a rough idle. I think there may be a picture of the EGR valve in the Tech Tips tutorial on cleaning it, but DON"T block it.

    Is your coolant level holding steady?

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    Raze's Avatar
    Raze is offline Cadillac Owners Enthusiast
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    Re: 99" Sts, Rough Idle When Cold. Help!!!

    Naw saw this symptom for almost a year with a partially lifted head, would allow just enough of a compression drop to miss until everything warmend up and sealed itself up, do yourself a favor, go down to a radiator shop and get a dye test of your coolant for hydrocarbon (combustion gasses) presence in your coolant. If you have an air compressor you can do a leak down test which is far more accurate and may tell you if you have a problem with an intake, exhaust valve, piston ring or head gasket...

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    VIPERRACING is offline Cadillac Owners Member
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    Re: 99" Sts, Rough Idle When Cold. Help!!!

    Quote Originally Posted by Raze View Post
    Naw saw this symptom for almost a year with a partially lifted head, would allow just enough of a compression drop to miss until everything warmend up and sealed itself up, do yourself a favor, go down to a radiator shop and get a dye test of your coolant for hydrocarbon (combustion gasses) presence in your coolant. If you have an air compressor you can do a leak down test which is far more accurate and may tell you if you have a problem with an intake, exhaust valve, piston ring or head gasket...
    This is exactly what the car is doing. It only has a very rough idle on cold start ups or after it sits for a couple of hours after driving it and then it clears it self out after it warms up. Im totally baffled and frustrated. I just bought a new dts also. I really think that these engines are junk and that gm is ripping us off. For god sacks, 80k miles and its already starting to have problems like this, what a piece of shit. The bad thing is I buy all my cars new and I know that they have never been driven hard or abused. Oh well, thank you to all that has chimed in, you guys rock.

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