i got my manual 2001 civic lx 6 months ago and it runs slower now. it has 45000 miles on it. when i first started driving the car it was hella quick. in second gear at 4k rpms it would go around 45 mph. now it runs 37 mph at 4k. the accelaration has slowed down alot. im thinking its the trasmission or the clutch but im not so sure. i changed the spark plugs and put intake. i also bought that chip that connects to the air filter censor thats supposed to give it more hp but it doesnt seem to work. SOMEONE PLEASE HELP ME!

 

listen!!! take it to a mechanic, let them find out whats wrong and get it fixed,honestly thats all you can do, unless you want my stock 89 beater to walk all over you lol 50 at 5000rpm, but seriously its a new car and needs to be fixed and from the sound of it its out of your leage do feel bad i wont touch anything past 1995, just to complecated for me and i dont wanna mess it up, so i buy older lol

 

Well for starters take off that sensor thing (it just messes with the computer on the car) It might be a new air filter that you need or the catalytic converter, but i honestly wouldnt know for sure. Just take it to the mechanic if you are unsure of what it is and they can find the problem.