I have no clue on the filter although if you hit K&N's page they might have some info. As for the tach i might have a bit of help. The gas gauge is what gave me this bit of insight although one of the more exsperianced guys here might know better and i would listen to them over me. Now, i have noticed that if i turn on an acessory in my car that draws on the electrical system (and we all know how good they are in these cars) that my temp guage will jump. It is probably related to a ground issue or a somewhat worn altenator, but it doesn't affect the car in any real way (aside from cutting my cd player off when i hit the brakes sometimes.) This may be the same thing with the tach and temp guage, although i am not sure. If nothing else check around on the grounds and see that they are tight and not corroded.