Little Rough Idle at Cold Start

[akolodny]

Dear Cadillac Enthusiasts,

I have a 1998 Seville STS with around 93K miles. In the morning, when the engine is cold, it is sometimes a little rought at idle until it warms up. Is it time to tune?

-alan

[misfit6794]

Is it violent shaking when you first start it? Thats one of the first signs of a failing headgasket. But if it is just a slight misfire, I would swap out the plugs, fuel filter, etc.

[Ranger]

Probably due for plugs & wires. Stick with A/C Delco

[Raze]

get a hydrocarbon test done on the coolant, let you know if there's a headgasket problem, I had the same symptom on my 98 ETC for over a year before I popped the head...

[Bigsnow]

Might be intake manifold plenum gasket. They can crack and leak causing rough idle and poor mileage.

Don't rule out condensation in gas tank. Especially when tank is low and during humid weather.

[scl98sts]

i am having a similar problem. a shaking thats pretty bad,but then it goes away.it has always had a little rough idle,i changed the iat motor ? helped for like a week, now it shakes really bad when started and when idle at red lights. when i mash the gas it bogs down,backfires motor whines ,not revivng high and then starts to go.under normal acceleration it just has a little hesitation. please help i have a 500 mile road trip in a day

[egheorghe]

I have pretty much the same problem. I just bought a 98 Deville 102.000 mi and when i start in the morning, idle fluctuates in between 1000 rpm and 850 rpm (it doesn't sound too bad) until it warms up. When is warm, it settles at 650/ 625. I do get poor mileage 12 mpg in the city and 16-17 on the highway.
i changed the air filter and checked the FPR (no visible leaks). How can i clean the manifold? Is it a do it by yourself thing? I still have my old Caddy (94 Deville- 220.000 mi) and i never had these kind of problems,,, or code P0741 witch i have on the 98.
I'm new on the forum and i don't know how to open a thread.
please help!

[Ranger]

Open a new thread with the "NEW THREAD" button at the top left of the page. Don't worry about cleaning the manifold. Clean the TB. Do a search for how to do it. There may be a tutorial in the Tech Tips section.

[submariner409]

Bigsnow.......No "plenum" on pre-2000. What's your car, engine, year, mileage ???

Every question in posts #1,5,6, and 7 is answered in here and Northstar performance.