New spark plugs cause a whistle?
 

alright i just replaced my spark plugs and my car runs great! but on occasion when i am in park and i rev the engine as soon as the rpms peak and fall my engine emits a extreemely high pitch whistle for about 2 seconds. if i rev it a lot of times over and over it will eventually stop but i was wondering what would cause it?

Aight first off I forgive you for calling your Jeep a "car" :icon_rolleyes::naughty::cursing:. Secondly did you do anything else, like with your Jeeps intake? Thirdly check to make sure you dont have any leaks around your spark plugs.

Was this spark plug installation using NEW spark plugs ?

Reason, new spark plugs come with sealing washers that compress when tightened down into the S.P. hole and seal the threaded hole so that it's gas tight.

If, after being installed, the plug/s is removed and then reinstalled, the sealing washer has lost it's ability to seal the thread joint.

Solution, purchase 6 new spark plug washers, remove the already compressed washers, and reinstall the S.P./s with the new washers.

well first off i pray to the cherokee gods for for forgiveness in calling a jeep a car haha. secondly in my XJ we used 6 brand new autolite copper spark plugs and put anti seize on the threads. and we did not take anything out except the spark plugs...we did change them while the engine was hot....

there is a little insulation around the nose of the intake (where the air comes into the box) and if it is peeling off, that would do it, also if you run a K&N or simmilar filter in the stock air box, this is common. mine does this when i rev it to 3500+ and let off the gas. not problems there, also could check for cracked vacuum line or unplugged one. one more thing it could be is the brake booster vacuum hose