Hi, my 2002 malibu hesitate and whistle when I accelerate. It only works fine under 20mph, but when it exceed, it whistles and hesitate on accelerating. On highway, it barely goes up to 60mph and when going uphill, it decelerates. I have checked the codes, I got 300, 404 and 443. Please help!! Thank you very much!

Hi,
Code 300= multiple cylinder misfiring detected
Code 404= EGR valve position sensor circut fault (could mean bad EGR valve or tube leak)
Code 443= EVAP VMV circut fault

All these codes could be a by product of the real problem which I suspect is mechanical in nature.
The whistling sound you hear is what concerns me. That sound is usually due to your engine sucking air from either a leaking intake manifold gasket, a leaking plenum gasket, a leaking or cracked / broken vaccuum line / air hose, or air intake hose is off or loose. Check all your vaccum hoses / plastic lines especially the rubber connecting boots and 90 degree boot connectors and your air filter, filter box is sealed and air intake hose from air filter box is tight / air filter not restricted. If all those look ok, spray starting fluid around intake to engine mating surface where gasket is while motor is idling. if it revs up, locate that area and spray it several times verifying motor revs up each time. That would indicate a leak in the gasket. Do this also for the intake plenum, but do not spray near the air intake hose from air filter box or throttle body.
See if any of those isolate a problem and let us know if you find anything......Mike

Whistle noise indicates a major vacuum leak. Maybe something loose in the intake system. Maybe a vacuum hose disconnected. Will explain lose of power also.