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I have limited experience with cars. I bought a 2001 Mazda 626 to commute to and from school a few weeks ago. Today when merging on the freeway I noticed that the engine sounded like it was working too hard and was turning at between 4,000 and 4,500 RPMs at 60-65 MPH. At one point the car let out a single violent jerk (no change in driving/RPMs before and after). Off the freeway acceleration was poor and rough. I parked it, went inside, had a panic attack, and then took it for a second test drive. It was fine after having sat for about 10-15 minutes.

The previous owner reported experiencing this problem 1-2 times. He had taken it to a mechanic prior to selling it to get a recommendation on the transmission, but the problem could not be reproduced in test drives. Fluid levels were good. The seller gave me the maintenance records, should I call the same mechanic or seek a different one? Should I request that the mechanic do more than test drive the vehicle to try to diagnose a possible transmission problem that is presently inconsistent?

Thank you.

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That rev range does sound high. It's sounds like the transmission is trying to shift to overdrive (the highest drive gear) but isn't succeeding (scary jerk but no change in speed).

Some internet research indicates that the CD4E transmission in the automatic 626s from that era could have potential problems. However, reading further, I begin to wonder if there could be a user interface or a computer problem.

For example, that link cites potential problems with the Hold button and / or O/D light. If the car is convinced that you want it to stay in a lower gear (i.e., via a faulty Hold button), it could produce symptoms similar to what you describe.

If this situation occurs again (or frequently), I would try

  1. Manually shifting gears (i.e., down into 3 and back to 4) to see if that resets the computer or sensor.
  2. Clicking the hold / overdrive button to see if it's stuck.
  3. Parking, turning off the car, counting to ten and restarting (much like you did the first time).

If any of the above works, that would indicate to me that there is a computer, control or wiring issue, not a problem with the transmission. With modern cars (of which this is one), it's very easy for the mechanic to scan error or sensor codes via the OBD-II port.

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I looked at the maintenance record again from when the transmission was last inspected and it was indeed brought in specifically for "no OD." There was a "scan test" in addition to multiple test drives. I also remember the seller saying that the second time he encountered this problem he tried #3 with success (like me). I sadly had to read about the Hold button in the owner's manual, but now that I know where it is and what it does, I will also try #2. This is very helpful, thank you! :) –  Jessica Jul 12 '12 at 19:13
    
@Jessica, you're welcome. Good luck! –  Bob Cross Jul 12 '12 at 20:06
2  
Over the past month I continued to experience this problem on the freeway with increasing frequency. Solution #3 worked almost without fail. I sought some input from a couple of different shops and chose the one who agreed it could be a computer or sensor problem. Fortunately they were able to replicate the problem by this point. Turns out it was a turbine speed sensor that needed to be replaced. I am happy I posted here because I had a better sense of what could be wrong, and this helped me narrow down my choices and find a great mechanic in my area. Thanks again! –  Jessica Aug 28 '12 at 21:12
    
@Jessica, that's great! Congrats! –  Bob Cross Aug 29 '12 at 12:42

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