Car shudders going thru an engine speed range of about about 300-500 rpm in the top 3 gears when lightly pulling. does not start until engine is warm. it starts around 1100-1300 rpm. A faulty O2 sensor was replaced and greatly decreased but gradually started up again. can't be sure if it occurs when rapidly accelerating and passing quickly thru the rpm band. Local distributor couldn't solve. They called mitsubishi service who suggested bad transmission fluid. Car is 2004 and out of warrenty but is 6000 miles short of first recommended fluid change and the fluid is clear red with no burned smell. Mitsubishi suggested fuid flush and change @$150. They also thought the sensor change would correct problem. what do you know?

Engine excelerates find but shudders while matianing speed

Answer: First scan the PCM for trouble codes using a hand held engine scanner, Then repair codes by replacing failed sensor as needed. If no codes are present then what is happening is the electrical component inside the MAF sensor becomes contaminated by the impurities in the air. These containments imbed themselves to electrical component that senses the air flow causing the sensor to be slightly off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the MAF sensor with a new sensor and you're problem should go away, plus your car get better mileage and performance. (Mass Air Flow MAF sensor or Air Intake Sensor AIS, depending on manufacture. It does the same thing with different names). I dont have the specifics on hand, but before replacement,(cause it is a little pricey) the MAF can be tested using a voltmeter. Tying into the signal wire, again, dont have specific color code on hand, but typically at idle signal should read .6 to .8 volts and when rpms climb the volts should climb to a max of 2.0 to 2.2 volts. Any reputable repair shop should be able to test this part if this explantion scares you. Hope this helps