car is sluggish and drops off on heavy accel.
Have several codes, po455 large evap leak and p0688 engine control relay short to positive, While monitoring datastream the throttle % dies off at WOT about 16% indicated when fully depressed, it is smooth til about 50% depressed and drops off. does this car have pedal sensor and a tps? is the tps integral to throttle valve?
this is most likely a MAF sensor failure or your evap system has a leak or faulty pump.Check all the evap lines from the tank all the way back to the engine. Most of the time a drop off like this happens its almost always a sensor in the air flow system or vacuum leak in the lines. Go over all the vacum lines under the hood as well.
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