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Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 24139
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1999 Mazda B2500: pickup..4 cylinder /8 spark plugs..tune

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I have a 1999 Mazda B2500 pickup with 4 cylinder /8 spark plugs. Last tune-up was a year ago. I rarely drive it (maybe twice a month). It starts up just fine. It even idles ok. The problem started a couple of weeks ago and got progessively worse. When I press the accelerator the rpms drops then raises by itself but will hardly make it beyond 2000 rpms before it drops again by itself. I thought it was bad fuel and just replaced the fuel filter , put in an octane booster and fuel treatment but no improvement. Any idea what may be causing this problem?
Greetings! You could have a bad mass air flow sensor. Or the snorkel from the mass air flow sensor to the throttle body could be ripped. Both are very common and can cause you vehicle to loose power along with many other drive ability issues. First look for cracks or rips or anywhere air can enter the engine that is not accounted for by the mass air flow sensor. Next comes the Mass Air Flow (MAF) sensor. This is a very important sensor input to the computer. It uses a hot wire sensing element to measure the amount of air entering the engine. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio. If the sensor is bad than this air/fuel ratio will be off causing severe performance issues. In extreme cases, I have seen these two problems cause a no start condition. This input can also be used in determining transmission Electronic Pressure Control, shift and torque converter clutch scheduling. The check engine light may even pop on if the sensor is bad, the snorkel is ripped or a tube has fallen off. This will result in a lean condition.
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