Changed Mass Air Flow sensor, CEL still displays problem
I have a 2000 Pontiac GTP (sc), 6 months ago, car stopped in the middle of the freeway for no apparent reason. Mechanic friend messed with car for awhile and as a last resort unplugged my Mass Airflow Sensor. As soon as this unit was unplugged, car ran perfect (even got better gas mileage oddly enough) Recently the CEL came on. CEL code stated I had a bad Mass Airflow sensor. Changed sensor, plugged it in... car wouldnt start! JOY!. However, car will run without the unit unplugged perfectly fine.
On top of this, the car has now started this wonderful ''shaking'' only when the car is in drive. Every once in awhile, when i release my foot off the gas pedal the RPM gauge will also randomly shoot from 1000 to 4000 and rock back and forth shaking the car while it does this until i place my foot back on the gas pedal again...
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Re: Changed Mass Air Flow sensor, CEL still displays...
It almost sounds like a fouled fuel injector. this is a tricky problem because it involve so many different operations. the maf is used to deliver fuel and the o2 sensor tells how much. there are 2 o2 sensors one before cat 1 after. mabey check these out visually. the computer should pick these sensors up if there bad. is this a supercharged engine? ill try to come up with some other ideas for you soon.
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I would replace the TPS sensor. If you have fuel pressure enough to start the car, then you probably have pressure always. Before turning the key to start, turn to ON. You should hear the fuel pump pressurizing the lines. Turn the car back off. Go under the hood and remove the cap to the Schrader Valve. Use a rag to catch any fuel when you depress the valve stem. If fuel comes out into your rag, you should have pressure. Try this a second time to be sure. I had this issue with my car shutting down. TPS sensor replacement fixed it. BUT...it could be vacuum lines, or another sensor fault. The TPS is a common issue. You may also want to clean your Mass Air Flow sensor with the proper solvent and technique.
Well there are several things that could cause this problem...
1. one of the coils may not be firing.
2. the ignition module could be bad.
3. the mass air flow sensor could be tellign the car to run rich (too much gas)
4. if the car is equiped with a map sensor it could do the same as a mass air flow sensor.
5. fuel pressure regulator could be leaking at vacuum port drawing in more fuel than needed.
6. the computer itself could be bad as well.
The car either has a map sensor or mass air flow not both. The mass air flow would be right after the air cleaner housing usually a 4 wire connector. map sensor is normally located on the rear of the upper intake manifold with 1 vacuum line going to it with 3 wire connector. Hope this helps.