Hello again guys, i know this is the second time i'm brining this up but i couldnt find any solutions for my problem yet. I have a big problem with my car, i'll briefly explain it.

This doesnt happen when i drive for the first 30 minutes, after 30 miuntes, my s2k looses half of the power. It gets harder to drive, the vtec gives less power, specially between 1500-5000 rpm, there's no power at all. When i change gear and i press the gas pedal it doesnt response. Sometimes when i go in low rpm such as 2500-3000 i press the pedal to accelerate, nothing happens just sounds weird like the engine is trying but can't accelerate, then suddenly it accelerates.
What's going on with my car?! i use the best petrol, the car's at 24K miles, everythings standard on the engine, standard injectors, air filter, sparks etc...

What might be the reason for this? What can i do?
I'd appreciate any help, please help me!

 

PS My car is year 2001 model with midified manifold and exhaust.

 

what exactly is modified? if you've ran leaded fuel, there's a possibility you've damaged the primary o2 sensor. there could be a bunch of things wrong, is there any mechanic in your area that can look over the car? run some tests? compression, leak-down, etc?

 

I will get it checked soon, i'm changing the sparks now to Greddy Irıdium to see whats gonna happen, than i'll ask your help again , thanks!