I just replaced the sparklugs and it seems that the car does not iddle smoothly as before. I stay around 800rmp for 10 sec then drops to 500rmp for 2-3 sec then back to 800rpm again. As the rpm drops the 2 fans in front of the radiator go On but go off then the rev. climbs. My question is, can the new plugs cause this irratic iddle? Or something else? BTW I used copper core plugs made by NGK. Any suggestion is greatly appreciated.

Larry
'92 190E 2.6 103K