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03 impala egr valve bucking during acceleration

03 impala 3.4 has been jerking for a month between 20-25 mph and stuttering at cruise above 70. Unplugged EGR valve and it stopped. Installed new EGR valve and plugged it back in and the jerking started again. Any ideas? Only code I have had is po336 for crankshaft position sensor and I had both replaced. 24x and 3x.
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Comments

  • edited January 2011
    Sounds like a partially plugged cat. Need to test backpressure at upstream O2.
  • edited January 2011
    Is the P0336 code still present or not. You only say that you had a code - not that you still do.

    Assuming that you now have no codes - the EGR is not a part. Its a whole system. There is a feeder system from the exhaust to the valve. There are the openings into the intake. There is a wiring/power supply for the valve. There is often a sensor and control solenoid, but I think that in your system those things might be integrated into the valve - not sure but you need to get the specifics of your EGR system operation and check the entire system
  • edited January 2011
    The PO 336 is still present after the crankshaft position sensors were changed. Mechanic said he did a crank relearn. There was no difference in performance after these were replaced. Is the EGR feeder system the EGR line (metal line)? The opening in the intake seemed nice and clear and I opening of EGR was also but could be stopped up near exhaust opening. I will take EGR line off completely and check.
  • edited January 2011
    2003 Impala 3.4. 159k. Catalytic converter replaced today. Mechanic scanned but no codes at all. Car runs much better and smoother but still slight jerk between 20-25 mph after 1/4 on temp gauge. Mechanic said O2 sensors are fine. The car still stops jerking when I unplug EGR. All the openings are clean into manifold and EGR line is clear and in good shape, wiring is good also. I have replaced TPS sensor, EGR valve, crankshaft position sensors, cat, trans fluid and filter change. I cleaned the MAF sensor with MAF cleaner and the wires look perfect. One was black with soot when I cleaned it but now it is shiny (I did not touch the wires at all, just sprayed with MAF cleaner). After I got home from CAT replacement I unplugged the MAF harness while the EGR was plugged in and the jerking went away also. Could the MAF be bad without throwing a codde, and could it cause the slight jerk between 20-25? The idle changes (lower) when I unplug the MAF sensor. I appreciate any info as the car is getting in my head at this point.
  • edited January 2011
    Has anyone ever driven this car while connected to a scantool to get live data? You still have a crank position sensor problem too. At this point someone with a scantool and a lot of savvy with driveability problems should have a gander at it.
  • edited January 2011
    Just wanted to post that it wss my Mass Air Flow Sensor the entire time. I had cleaned it with the MAF cleaner but it was somehow acting up without throwing a code. I replaced it with an original salvage yard pull, cleaned it up and it drives like new. No jerking or hesitating at all and the power feels much better also.
  • edited January 2011
    Thanks much for the follow up report. Its always great to hear how things played out.

    Of course, I often like to learn something at that point. So I'm wondering if anyone has any ideas about how you get those symptoms with a P0336, a "cure" from and EGR disconnect while the problem is really in the MAF - ? Weird.
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