need help asap

started my car one day and it ran funny...it idles at about 600 rpm's and just goes up and down up and down between 600-800...the code reads PO:100....Mass AIr Flow Sensor...had it replaced and it still says check engine and still runs bad....it also spudders sometimes when i hit the gas...or when i just rev it up it spudders then goes up and the BOV goes off...whenever i am going uphill it dies...not all the time but some of the time...i have a new Walbro 255 fuel pump so that cant be the problem...i also got out of my car one night and my exhuast we cherry red...but just at the muffler??...i have a bad exhuast leak right now but im sure thats not causing any of this...please help asap Thanks in advance.
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Sounds too rich. Are you sure the sensor was replaced? HAs anyone checked the wiring between the sensor and the ECU? You can use the ECU pinout and the diagrams for 2g MAS in a 1g from www.vfaq.com to figure it out I'm sure. If the mas is good for sure, and the wiring is fine, we're screwed.

it is running very rich, would that be every problem?? idling and all...my back end is BLACK!...i'll have to check the wiring...i bought a USED MAS but the guys at a perfomance shop here said it was still good..i'll have to check the wiring...if all thats fine...what else could it be...or would the engine just be F*ckd

do you have a aftermarket fuel pump regulator to control the overrun from your walbro 255? check the faq kevin wrote out all the reasons why you need one and not having one will make you run rich

The 255 with no reg is certainly making things worse. But on its own its not enough to make the car undriveable. It will typically just max out the trims on the lean end.

You should never assume that just because you replaced a part, that part can NOT be the problem. It sure can ;) Replace the sensor again, with a known good one. Check the wiring first though, a short in the harness somewhere could blow out good sensors, and you'll never get anywhere.

Turn the car off. Unplug the ECU harness connectors (4 of them, behind drivers side center console panel). Unplug the MAS. Using an Ohm meter, check each pin on the MAS connector to every other pin on the MAS connector. Repeat for all pins. This will at least rule out a short in that part of the harness. In fact if it passes this simple test I would be comfortable going ahead and trying another MAS.

Edit> This is where a logger would come in handy, and why I recomend everyone should have one. ;) You would easily be able to check intake air temp, baro pressure signal, and airflow itself, to determine if the MAS is the cause of the problems. ;)

i dont think its the MAS anymore...i start my car and smoke comes from where the o2 sensor goes into the exhuast manifold..i ordered a new one so hopefully once i get my new one in the problem will be solved.

I've never seen a bad sensor allow smoke to pass. I dont think its possible. But replacing that sensor is a good idea, and I'm glad youre doing it. One more thing eliminated. ;)