I recently bought an 03 6 speed .... 5th gen maxima, its has k&n intake and full stainless exhaust, for a few weeks it ran like a demon torque steer aside.. for some reason it now seems to not have the really strong power boost (broadband) that it initially had!! It would kick in around 3200 or so and run all the way through the range and stay there as I shifted then kept on pushing. I've pulled a p1800 code .. solenoid etc... I swapped that out and still the issue remains!! Has anyone heard of this elusive HITACHI BOOST CONTROLLER and where is it located? The only Hitachi anything I can find is on my throttle body and I cant figure this out please help??

 

1800 is VIAS solenoid which, if it is not functioning, will affect performance between 1800 and 3600 RPM.

If you've already replaced the solenoid you need to check the wiring. It's just +12V to the solenoid, and one wire to the ECU

 

+1. The solenoid is non-polar (as in, doesnt matter which prong gets positive or negative for it to function), so electronically speaking your only concern is that the power wire from the ECU is actually providing power. Mechanically speaking, it is also very simple - You can test solenoid function by jumping a wire from the positive battery post to one of the solenoid prongs; if it clicks when juice is applied, the solenoid is functioning as intended, where as no clicking would indicate the solenoid is faulty and must be replaced entirely. The last factor would be vacuum, as the solenoid controls a valve inside the intake manifold via vacuum. Make sure that your vacuum lines are connected properly (consult the FSM because i dont remember what tubes go to what hoses). If they are backwards, it wont function properly and youd probably have the exact problem you have now. Also check that your vacuum lines are not cracked, disconnected, or otherwise leaking.