98 mazda 626..starts then shakes and then shuts off

A few things could be causing this problem:

1. Vibration when running is an indication that one or more spark plugs are fouled or missing
2. Cracked/worn distributor cap
3. On all models except the Millenia, the fuel filter is attached to a bracket located in the left rear of the engine compartment, next to or beneath the brake master cylinder fluid reservoir

Yes, I had the same problem with a customers car, the idle air control solenoid sticks, causing low idle and even stalling if you are running ac. Remove the IAC with the small aluminum housing it is attached to (4 screws), remove the idle solenoid a round looking device, 2 screws hold it to the housing. Carefully pull it apart and clean out the inside with carburetor cleaner, there is a spring and plunger inside there, make sure the seat is clean where it makes contact inside the housing, this valve controls idle through vacuum, if it is weak or leaking, through carbon build up it will cause the engine to vibrate because of very low idle. Also which I did on my friends car I pulled out on the spring and stretched it to make it push tighter against the plunger, this created a better seal, once I refitted this to the car it was fine. That valve was $250.00 my cost, which is why I went to this length to correct. Most shops would have just fitted a new valve. I may also add, I know of a lot of customers changing all of their motor mounts for the vibration problem when all they need was a little boost on the idle, which is non adjustable.

I have my mazda capella 1994 model 2.0 petrol sedan, the rpm get dropped i already change the inlet gasket but still rpm dropping ang engine running is un equal idling when you are in low rpm, is there any connection with the valve or computer box ?