I think I might have a problem or maybe I just haven't been paying attention. I installed my NGK Iridium IX plugs about a week ago and now I notice when I am stopped my Red Line limit is at ~4000 rmp. I have never notice this before and think it has just arose since I put the plugs in. It is really weird if I am stopped it doesn't matter if I am in park or neutral it is limited to 4000 rpm but if the car is rolling in neutral (needs to be rolling about 8mph) it is limited at ~5500 rpm. As far a I remember the limit always use to be a 5500 but I might be wrong.

That is because it is pre-designed into your ECM Chip not to rev higher than that in park, so you don't blow the engine apart! It all started years ago when when some dumbass reved a Park Avenue in park upto 6500 rpms & then the engine blew while the customer was "test driving" the car in a Dealer'* lot!

Does it monitor the speed of the car? I have never noticed it only being at 4000 when it was not moving but like I said I might not have been paying attention and I might of never tried to red line it when it was standing still before. I was just letting one of my friends hear it today and it was the first time I noticed it.

WOW! I learn something everyday. I have had my 96' for over a year now and rev it up all the time and this is the first time I noticed a lower limit when the car in not moving. I was driving myself crazy all day trying to figure out how the plugs could effect this and could never come up with anything. I guess I was right.

Revving your engine out of gear (P or N) is bad news. Don't do it.