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99 STS Lumpy Idle


BritCaddy

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Is it normal for the N* on the STS to have a lumpy idle? When I'm sat in the car with the engine idling, I can feel the car vibrating erratically, like it has a misfire on one cylinder. When you look at the engine you can see it shake occasionally on its mounts. I changed the ignition leads, but it made no difference.

Before I start to throw money at it, has anyone else experienced this and how did you fix it? Thanks.

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Check for codes that might be set, to see if you are getting a P0300 misfire code.

Try looking at the engine in the pitch dark and see if you are getting any arching

Pull the plugs and see if you have any cracked plugs are missing platinum pads or damaged plugs

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Uh, no.

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Is it normal for the N* on the STS to have a lumpy idle?

There have been occassions while sitting at a traffic light that I had to concentrate a bit to hear the engine because sometimes it's so smooth and quite that I think it may have stalled. Of course, everything was fine. If it did stall, I believe the DIC would tell me.

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If you've ever been at a traffic light and for a moment thought your car stalled so you turn your head quickly a to try to listen and said to yourself...Did it just stall? :huh: Then you looked at the tach and notice the needle is locked at 600rpm. That's what happened to me on a few occasions. With an engine with over 200,000 miles no less. B)

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Mine has been doing that ever since I bought it. Mine is a 2002 and I'm guessing it may be the converter, but I'm not sure. I've down absouletly everything to get the idle fixed, but nothing helps. Yours is a 99 so I'm not sure what it could be. Some guy earlier had mentioned his being a 98 and he replaced the O2 sensors.

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