Rep Power: 0

I have a 2000 ek coupe d16y5 with intake and header back exhaust. Heres my biggest problem. When i start my car i always let it warm up. I drive for a few minutes and everythings fine. Then it acts up and wont rev past 4k. I have 3 cel codes. Vtec circuit fault and both o2 sensors. Im working on trying to fix the problems. Tomorrow im putting the new primary o2 sensor on and a new IAT sensor. Im not sure if thats going to fix my problem or not but in wondering what you guys think

 
Rep Power: 0

Oh and i forgot to say my buddy let me put his IAT sensor on and i ran it for about 2 miles and everything seemed ok but im not sure if i drove it far enough

 
Rep Power: 156

this is probably the issue. check your oil level and see if it's low. if it's too low then there isn't enough oil to push through the vtec solenoid so the vtec doesn't engage. it usually engages around 3700-4000 RPMs.