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Okay folks this will be a strange one for you.

04' Deville 167000 miles ran great smooth and great gas mileage.

One day the idle was running high so I replaced the ICM and it took the idle down but seems too low at about 675 in gear while stopped. (I think it's too low)

From this point the car now has other issues I've never experienced before the ICM issue.

First, when cold start the engine seems like it's laboring more with vibration and acceleration. Even after it warms up I still feel the engine more then I use to but not an absolute miss. There are no misfire codes and while it warms up it runs a little smother.

I can hear a rattle coming from the engine when just starting out in drive but it goes away if I accelerate a little more. At higher acceleration the rattle comes back until I let off the gas.

Sometimes at about 2600 RPM it feels like it's slightly missing but not a consistent miss is noticed. Maybe more like a  very slight stumbling sensation.

The weird part is when I shut it off after driving for a while.....

When I start it up, maybe after setting for 20 or 30 minutes it runs like it did before the ICM issue. Quiet, silky smooth for about 10 minutes. After that, it starts feeling like its working harder and I can again feel and hear the engine more inside the car.

Another thing that came up lately was a loud hiss and gurgling noise when starting it cold coming from the plenum and firewall area. After warming up it goes away mostly. I disconnected and plugged the vacuum hose going from the valve cover to under the plenum and that stopped all the noises. I'm sure that is not a good fix but it works for now.

I also know the secondary air pump is toast so I can live with the check engine light for now.

I'm stumped....I am on a fixed income so taking it to a dealer is not a affordable option. I've always worked on my own cars so I hope this is something that I can handle.

Please give me some ideas of where to look.

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@Tim Mahoney

The most important thing to do at this point is to check for codes

Go to this link and follow the directions for the 2000 to 2005 Deville on how to retrieve codes and post them here.  Have a pencil ready to write them down or video tape them on a smart phone they come fast. Restart the code dump again if you miss any.  Note and also write down if they are Current or History codes.  You will see codes for a lot of different systems we are looking for P or powertrain codes specifically

Post them here and we can help better

http://www.caddyinfo.com/readingcodes.html

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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