Engine bogs at 3000 rpm under load or past 40% throttle or 4000 rpm no load

[Soravia]

I just redid the entire intake manifold on my KA24DE on the 91 240sx. I checked all the vaccume hoses and replaced them where they are worn or crinked. I believe the MAFS is fine because the car idles and runs fine on anything other than past 3000 rpm under load. It has been cleaned with MAFS cleaner. Used that on the IAVC as well.The throttle position sesor TPS resistance and volts have been checked with a multi-meter.Coolent sensor works fine as well.Oil and filter was changed about 200 miles ago.Knock sensor was replaced.All the EGR components were removed and the two plugs at the end of the engine were unplugged. Only the IACV and related parts were left.The spark plugs (NGK) and O2 sensor are also new.The throttle body also responds just fine as well.Timing chain guides were removed about 1000 miles ago and the tensioner was also cleaned up.The only noise I hear is a little bit of valve lifter noise (not too loud). I just put in half a bottle of SeaFoam into the engine oil to fix that.

What could be causing the engine to bog down like it's mis-firing past 3000 rpm under load? With no load the tech would jump up and down when it gets near 4000 rpm, although I do not hear any knocking (detonation) noise from the engine.If I press hard on the engine there would be bogging and it would just die past 60% throttle.

Could someone please give me a clue why it might be acting like that?

BTW. I fixed the PCV hoses that go into the upper manifold so the engine idles very smoothly now. I'm not sure about the timing on the distributor but I adjusted it while listening to the engine. Retarding it a bit doesn't change anything and if I advance the timing a bit the car idles like crap.

[nismoracingsx]

alot of hesitations around 3k are caused by grounding problems (so i've heard) search for diy grounding kits, someone has a writeup on it. Also has tips on checking your grounds, etc. good luck.