One problem related to crankcase (pcv) has been reported for the 1999 Mazda 626. The most recently reported issues are listed below.
I purchased a crankshaft pulley for my 99 Mazda 626 on 06/01/04 & had it installed. On 07/10/04 the same part broke again & had to be replaced. This cost me $1100 in less than 2 months. The shop that repaired my vehicle the 2nd time informed me that when they ordered the part from Mazda, they were advised that they can't keep this part on the shelf. Since Mazda is aware of this problem-they need to take action to help the owners of these vehicles.