I've got a 1991 base model Stealth, and I was wondering if putting the K&N air intake upgrade would have any major negative effects to the car. I had been told that changing the air intake system would screw up the MAF somehow or another, but this was never really explained to me.

Thanks for the help guys

 

not much would actually change. At least no negative effect. There would be a better throttle response and it might rev easier. But if you are going to do a true cold air intake you will need to route air from outside to it and seal off the filter from the engine.
I have a simile reusable air filter on mine, but it was not set up as a cold air intake. If you look you will notice that half of the air that it gets is form under the hood, thus it's more like hot air intake lol. Some fresh air gets trough but no where near to be cold air.