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I have an 03 cts 3.6 and it has about 160k mi on it. Recently it has started to idle roughly when I stop at Red lights, and sometimes it will continue after I accelerate again causing a nasty vibration and the occasional blinking check engine light. However if I can manage to turn the car on, go, and keep the rpm up the car will run fine until I have to stop. It also seems like if it's running poorly I can pull over and restart my car and it will start to run smoothly again until the dreaded idle

I had a problem with similar symptoms a year or 2 ago. From what I remember it was a rough idle and similar vibration in acceleration along with the blinking check engine light (it was misfire warnings before and although I haven't checked this time that is what I suspect). I took the car to my mechanic where he found and replaced a bad coil pack. It cost me almost 500 bucks and I know Cadillac parts are expensive and mechanic has to make a living, but being a senior in college I don't have 500 bucks laying around and would also like to learn something if I can.

Now I don't have much experience with fixing cars. I have done a brake job or two on it as well as replacing the alternator, serpentine belt, and tensioner pulley, but that's the extent of my familiarity with the inner workings of this car. Any advice you have, diagnosis, mistakes, parts/brands to search out or to stay away from, ways to prevent it from happening again, resources on video, maybe even a walk through would be much appreciated.

Mike
 

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2005 CTS/ 2008 DTS/ 2008 STS V8 N*/ 2011 CTS4 ALL W/D Pearl
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First find out what codes it is throwing.

It sounds like it might be a simple coil again. You can easily do this repair yourself for $40-$80 depending how much you pay for the new coil.

Some of the coils can be accessed without removing the intake. If you are that fortunate you can change one in 10 minutes.

I have no idea what you paid $500 for before?
 

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Discussion Starter #4
Last time I had to replace a coil pack. I've priced those out a bit and they seem to go for around 170 bucks.

And would that be 3.2L then? Engine is stock
 

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'05 CTS-V
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Last time I had to replace a coil pack. I've priced those out a bit and they seem to go for around 170 bucks.
I'm not sure where you're pricing them, but check www.rockauto.com and you can get them for 1/4 - 1/2 of that. And you can probably take the part numbers you find on rockauto.com and find them even cheaper on Amazon.

A blinking CEL indicates a misfire, so it likely is another coil pack. Could also be the plugs themselves - were they replaced before? How many miles are on it?
 

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Discussion Starter #7
Ok so I had the codes pulled and there are quite a few. I'm getting p0058, p0161, p0318, p0300, p0302. I want to go ahead and replace the coil pack but the guy at the auto parts store is making me second guess my diagnosis

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The plugs have not been replaced since I've had the car and it has 160k on it. I've put abt 30k on it myself

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Also, cylinder two is on the right side of the engine when facing the car right? and are the O2 sensors different in different banks, or is it the same sensor in all 4 positions?
 

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I would just replace the plugs because they really aren't that expensive and they most likely haven't been replaced at all. If that doesn't work check which cylinder the misfire is on and change the appropriate coil pack. If that doesn't work it could be some kind of vacuum leak.

As for your O2 sensor question, there is two banks, one on either side of the car (I believe bank 2 is driver's side) and two sensors on each bank, one before the cat, one after. I doubt that is your problem though, especially if you aren't getting a code from it. Cylinder 2 is front of car, driver's side.
 

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I have a 2005 cadillac cts 3.6l, with around 100,000 miles. I went ahead and changed spark plugs last year, and then the battery died. the battery they asked for was not in stock and quite a hefty price. I read about other batter's with more cranking power that would work and fit a little bit taller in height so I bought it and replaced it. After about a week I would find I was having a rough idle when at a stop sign and the check engine light came on. It was misfiring on cylinder 1. We replaced the coil pack another spark plug and fuel injector. it made it about 65% better but still nor running like it should. When I brought it back, they told me I didn't tighten my battery cables tight enough, and sure enough it ran fine....for twenty minutes then was idling rough with a lack of power unless I stepped on the gas hard. Now I've tried the battery cable thing a few times and it would always work for about 10 minutes then back to rough idle. So after a while I pulled the codes again and it told me fuel injector 6, misfire 1, and oil pressure switch. Ive replaced all 6 coil packs, spark plugs and fuel injectors and new oil pressure switch and it was like we did nothing to the car. My question, is, with it working for a quick minute when I used to take off the battery cables and put them back on, which seems not to work anymore, whats the probability thats its the ecm. could that bigger battery damaged the ecm, people don't think so but im not sure. I find it funny that when the cables came off it, it would work for a minute then run like garbage. To me, someone who is not a mechanic, seems that its resetting it, then shorting out and back to rough idle. Any suggestions is extremely helpful
 
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