One problem related to vehicle shudder has been reported for the 1999 Mazda 626. The most recently reported issues are listed below.
I bought my 1999 Mazda 626lx used in June of 1999 with 39,000 miles on it and throughout the two years that I had it I've gotten serviced more times than I can even count. Over the past 8 months the problems with the car have been getting worse. Initally the car was shutting off occasionally whenever I came to a stop. That alone scared me and I feared driving on the interstate because of this. The mechanic told me that my spark plugs needed to be replaced so I did that but the same day that I got it fixed the same thing happened and car started driving very rough. Although the car has not shut off on me lately it has done some very weird things like driving while the car is in reverse. I parked the car one day in an awkward way so I wanted to correct myself and when I tried to reverse the car kept on driving forward (I'm lucky there wasn't another car in front of me) and it was hard to shift into park when I was finally able to do that I turned to car off but then couldn't get it to come back on so I had it towed to the dealership and they said it was a problem with the shift interlock gear. Since I 've gotten my car back it drives worse than ever before the transmission slips, I can only drive in overdrive, the car shakes when it shifts gears and at certain speeds it thrusts forward with so much force that I it feels like I've just been rear-ended. Fortunately, I haven't had to replace the transmission but after reading other reviews about this car I fear that the time maybe coming soon especially since I just reached 83,000+ miles. With all the complaints on this problem Mazda should really take action on this issue because these cars are unsafe to drive and personally I will never buy another Mazda again.