Question about 1993 Subaru Impreza

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Misfire/Backfire and not accelerating properly wondering whats the problem?

I was driving on a broken exaust right where my rear cat was and the fixed it (weld) then it start to not accelerate properly and then I found out that my air filter was kind of open it wasn't sealed properly so I sealed it meanwhile I have never changed my filter so maybe that's a problem? I also was revving the engine and I keep hearing this popping noise as soon as I press the pedal not all the time but occasionally. I went under the hood and found out that the popping noise sounds like its coming from air filter cabin anyone have any ideas on whats goin wrong with the car?

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1st get a new air filter I recommend a quality brand like the oem one or purolator.
2nd remove and clean the maf sensor. Start with the screw clamp on the intake hose. Then unplug the sensor just squeeze the tab and wiggle it off. Now remove the 4 - 10mm boltsthat hold the maf sensor on the air box. Use caution as some models have a housing with brackets that are loose when the above 4 bolts are removed.
Next clean the air flow sensor using crc maf cleaner or other maf sensor safe cleaner. This is necessary as the sensor gets dirty as the miles accumulate. Make sure the sensor wires are very clean and let it fry for 30 mins before re-installing the sensor.

I would inspect the blower motor for debris as a 93 impreza doesn't have a cabin filter.
You can access the hvac fan from under the glove box see the attached video for how to. I know its not the correct subaru but the procedure is the same. Misfire/Backfire and not accelerating properly won - misfire-backfire-not-accelerating-tq5sh21jzhkdedjt044n20r3-4-0.jpg

Posted on Dec 15, 2014

Testimonial: "i did tjis problem still occurring when im on the highway trying to quickly make it to work on time the rpm needle has problem getting me to the destination quick enough. what I mean is the rpm needle jumps up and down even tho my foot is holding steady pressure on the accelerator if I decide to give it a little more pressure it starts to make a popping noise sounds like its coming from cabin very confusing could it be from my throttle body?? throttle positioning sensor ?maybe"

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Check cam shaft timing, park plugs, HT leads. If all okay, backfiring is a sign of a lean mixture, can be the MAF sensor or low fuel pressure, fuel pump problems are very common, but also a MAF sensor broken contact.

Posted on Dec 15, 2014

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Air filter not sealed and never replaced, you should clean the MAF sensor since the dirt passes through the air filter.

Posted on Dec 15, 2014

Testimonial: "i did tjis problem still occurring when im on the highway trying to quickly make it to work on time the rpm needle has problem getting me to the destination quick enough. what I mean is the rpm needle jumps up and down even tho my foot is holding steady pressure on the accelerator if I decide to give it a little more pressure it starts to make a popping noise sounds like its coming from cabin very confusing could it be from my throttle body?? throttle positioning sensor ?maybe"

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You should spray with MAF/TB cleaner to clean throttle body(TB) too. While you're there, spray the IACV Intake Assist Control Valve. If your RPM fluctuates, most likely the carbon build up block the air to assist idling when engine is COLD. IACV is located at front/top of throttle body. If you found carbon dust build up in IACV, you solve your issue.

Posted on Jan 30, 2015

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Well i did not pass emissions a code 0420 came up when i go to push on the gas i takes a while to go so there is loss of power in my car


The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, ad sets a P0420, or a P0430, depending on which bank it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter.

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The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called.
By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust.
If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, or a P0430, depending on which bank it is.
To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely.
If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter.
You can try resetting the ECM by turning your ignition to the on position (engine not running) and pulling the fuse to your ECM for 30 seconds and then placing it back in. Once the fuse has been reinstalled, start the car and let it idle for 1 min and then go for a test drive.
The engine may stall when you restart it, let is stumble and stall. Just restart it, the ECM is relearning the sensors like it was the first start up the engine ever had then go for a test drive.
This should reset everything and turn your check engine light off, if the check engine light came back on, have it scanned again at Auto Zone, Parts source where they scan free of charge and address the issues the DTC codes points out.
The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those syptoms are there, the converter likely needs replacement.
Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc. If all that checks out, you'll want to check the operation of the O2 sensor. To do that, you'll need access to a scan tool or oscilliscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced as mentioned earlier.
Thank you for using Fixya and be safe.

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