: Northstar Cold idle Knock?

10-02-08, 03:53 PM
I noticed our '98 STS has been exhibiting a cold knock when it has just been started after sitting for a long while when the engine has cooled down. It is not terribly loud, but its definitely there and lasts maybe 2 minutes or a little longer. Once the motor is warmed up the knock goes away.

I have WOTed the thing at least to the point that the black smoke is gone and it's still there. Oil level appears to be ok. The car also has a light idle shake occasionally but I am not getting any cylinder misfires that I know of.

Car has 121k miles on the clock and previous owner appears to have maintenanced the car semi-regularly. Is this something I should dump the car for or is it not of large concern?


10-02-08, 04:45 PM
Sounds like piston slap aka cold carbon rap to me. A dose of WOT should have taken care of that.

10-02-08, 04:49 PM
Find a 20 oz. plastic bottle of Chevron TECHRON, dump it in the gas tank and fill up with 93 Chevron, Shell, or Texaco. Grab your bride/gf/whatever, hit the bank machine, and go for a long drive to include lunch in the boonies. Run the snot out of the car - don't tear the tires off, exercise the engine. Enjoy.

Google "techron" and "top tier gasolines".

10-02-08, 05:25 PM
I'll give that a shot Sub... Thanks for the advice. I absolutely love the N* when it's running properly. It's all the little quirks that are scary. I sure hope I don't have to get rid of this car because it's really fun to putter around in. 5th Seville I've owned so far.

However, if you guys think this could be indicative of a major problem, I may have to sell it before anything happens.

10-02-08, 07:02 PM
At 121K you're in the spark plug/wire department unless you or the previous owner had the job done somewhere between 80K - 100K. Scads of recent posts on pre-2000 Northstars, wires, coils, diagrams, etc. ACDelco 41-950 plugs, gap .050", torque 13 - 15 ft/lb.

A cold carbon or piston rap is the least of your worries.

10-02-08, 07:05 PM
My car does the same thing when cold, but I never worried about it since so much work was done to the motor before I bought it. However, I'll follow Sub's advice one day and see if that cures anything.