Bought the car about half a year ago. That time it did 180 kph with four passengers into little uphill, and that wasnt even topspeed . And now it ran only 160 in airfield, i was alone and it was a lot longer road.So a definite loss of power?

About a month ago something strange happened. I was driving a really bumpy road then suddenly my car had vtec! Before that i didnt have a noticeable vtec, but now there was strong and loud vtec at 6500 rpm. But also after that happened, it felt that low rpm torque was really bad and torque overall. Engine is d15z6 with 2' piping and exhaust manifold. That engine shouldn´t even have noticeable vtec? Previous owner has modded the ecu?

Any ideas what has happened or what should i do? i´m really confused

 

Has the car been properly maintained?

Reasons why your VTEC might not be working

 

i think i solved the problem. o2 sensor is broken and fast idle valve is loose.
Vtec sound was distinct and louder because exhaust was also little loose, i think?