Wee problem, i have a 2.0DOHC. Under acceleration (hard/normal) my car bogs down about 3k - 4k roughly then kinda frees up and the power is delivered again. I'm not sure what it is and i've checked my TPS and replaced my spark plugs.

i'm using a 1.8 exhaust system from the downpipe and a 1.8 downpipe. The thing is that there's two different 1.8 exhaust systems, one has smaller diameter pipes and a smaller flange on the downpipe. i'm using the bigger downpipe that fits the 2.0 manifold and the smaller 1.8 exhaust system which i've had to gungum the 'joint' to the downpipe to stop it blowing.

Could the exhaust system cause this lack of power? i'm thinking the smaller 1.8 exhaust system may not allow the gasses to escape as freely at that rev range as obviously the 2.0 produces a lot more power. I'm thinking that about 4k there's maybe too much back pressure or something?