I have a p0401 code, I replaced everything, one part at a time. First the egr valve, then modulator, then the VSV, now it runs, but I have to keep tapping the gas to Rev it up, unless I floor it, then it revs up normally. When it started running like that it threw the misfire on all cylinders codes. Idk what's going on, that's bad enough in the wgr system to do this.

 

P0401 if for insufficient EGR flow. Not enough flow doesn't normally cause engine operational problems. Too much EGR at the wrong time will cause the engine to run poorly or quit.

Check vacuum hoses for problems
Could be a bad MAF or ECU.

Bypass the VSV to turn the EGR on at engine idle. The engine should bog or quit from excess exhaust gas.

Disable the EGR and determine if the engine runs better.

The EGR system should be off under the conditions below:
Engine not warmed up.

Deceleration (throttle valve closed).

Light engine load, low intake air).
Engine idling.

Engine speed over 4,400 rpm.

High engine load (large intake air)