99" Sts, Rough Idle When Cold. Help!!!

VIPERRACING · #1 (**permalink**) 03-25-08, 03:32 PM

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.

submariner409 · #2 (**permalink**) 03-25-08, 05:30 PM

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.

VIPERRACING · #3 (**permalink**) 03-25-08, 11:51 PM

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.

Highline Cady · #4 (**permalink**) 03-26-08, 12:50 AM

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.

**Ranger** · #5 (**permalink**) 03-26-08, 11:31 AM

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?

Raze · #6 (**permalink**) 03-27-08, 11:30 PM

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...

VIPERRACING · #7 (**permalink**) 04-01-08, 03:19 PM

Quote:

Originally Posted by Raze

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.