1997 Toyota Corolla

Noises problem
1997 Toyota Corolla 4 cyl Front Wheel Drive Automatic 115000 miles

I changed the spark plugs in the car just as I have done before. I start the car and the engine knocks.
I think that maybe something was wrong with the new plugs so I put the old ones back in. The knock stays.
It is an overhead problem as it increases with RPM.

I checked the oil and its not low, although it could probably use a change (its my grandmas). The knock goes away when the car warmed up. I parked it to listen some more. I revved the car to 4k and it was fine.

I let the RPM's drop and it was ok for a few seconds. Then the car kind of choked and the rpms seemed to fluctuate low. The knock began again. I gassed it a little and the knock stayed.
March 20, 2010.

If all you did was change plugs, then you may have got the wires mixed up.

Mar 21, 2010.
I did them one at a time to make sure they stayed in sequence

Mar 21, 2010.
A knock would indicate a rod or main bearing. I don't know how changing plugs could cause this.
The wrong plug could actually hit the piston causing mechanical damage, but taking out the old plug, it would be evident that the plug was damaged, if so then debris may be in the combustion chamber.

Mar 22, 2010.