: Seville 03 shaking problems after tune-up.

07-03-09, 05:18 PM
I just changed the spark plugs on a Cadillac Seville SLS 03. As soon as I changed the spark plugs the car started to shake at idle (Did not do it before). I plugged the computer to check for codes and there are no codes. The spark plugs I used are Champion platinum and I gapped them correctly...
What could the problem be?

07-03-09, 05:45 PM
The plugs should be ACDelco #41-987 Professonal Platinum with the gap checked at .050". The coil boots should be checked for cleanliness and spring (internal connector) tension. The coil cassette ICM connectors and ground spring should be checked for cleanliness and proper contact. Make sure the PCV connections are secure. make sure the injector connectors are secure.

You do not need any external scanners or computers: it's already built into the car. Read the thread at the top of the Cadillac Technical Discussion page, Technical Tips, "How to pull codes on later................". learn to pull your codes and don't clear them - keep a log. If you clear codes within a few weeks of an emissions test the car will fail until the system resets to a "Ready" status.

Don't ask why the Northstars dislike anything other than AC plugs. It's black magic, but well documented in here.

07-13-09, 01:10 PM
Hey Thanks for the reply.
I changed the plugs to AC Delco, but the car still idles rough.
It does it mostly when I cold start the car, and it idles smooth sometimes.
I checked all of the issues you mentioned and everything seems alright. My bet is that it is the coil boots.
Please let me know what you think,
Thanks again.

07-13-09, 03:37 PM
Before you pull the coil cassettes again to check the boots, pull the engine beauty cover and go over the vacuum lines from the throttlebody to several sensors and switches. A bad rubber connector or cracked plastic line will give you an idle miss sometimes. (If a plastic vacuum line is broken, a piece of proper-size rubber vacuum hose from the blister pack displays at a parts store is just fine.) Check the larger plastic vacuum/supply lines for the PCV system, one at the rear cam cover which goes into the intake manifold behind the p/s pump reservoir, the other from the throttlebody casting to the driver's end of the front cam cover. Last but not least, start the car and shoot a tad of choke cleaner or starter fluid down in the area of the hose clamp screw between the throttlebody and intake manifold. Any idle speed change ?? Vacuum leak. There's a rubber bellows "plenum" connector there and they are known to crack and cause a nagging vacuum leak. Easy fix, $40 dealer part. Lots of posts, but c'mon back if that's it.

(What about that PITA rear A.I.R. valve - is the metal flex pipe OK and no exhaust leaks ??)

10-18-09, 11:27 PM

I didn't have time to go through the problem, thanks a lot for your reply.

My problem persists of a intermittent rough idle

I ended up changing the boots, but the car still idles rough from time to time.

I noticed there is a sound of an air leak coming from the engine. It seems to come from the area around the vacuum on the rear cam cover and the A.I.R valve area. When the engine is running, and I disconnect the vacuum hose on the rear cam cover, and block it with my finger (the hose) the air leaking sound goes away, but the hose seems fine. The car also consumes a lot of fuel (10 mpg mostly city), I think the problem is related...

What can the problem be???
Is it possible that it is the A.I.R valve?

Thanks a lot.

10-19-09, 08:06 AM
You'll have to locate the vacuum sound exactly by using a stethoscope and then read post #4 again. The vacuum fixes are all there.